Topic
River and lake questions for kids
Here are 204 questions about rivers, lakes and fresh water from 19 A Million Whys books, each with a short video answer. Book 19, The River Expedition is all about rivers, lakes and fresh water, and the rest come from other books in the series. Tap any question to watch the video and read the answer.
From Book 19: The River Expedition (150)
Where Does a River Begin?
Most rivers begin as tiny trickles, so small you could step right across them! Rain and melting snow soak into the ground, then seep back out at a spring or run downhill.
What Is a Tributary?
A tributary is a smaller stream or river that flows into a bigger one! Think of a tree: little twigs join into branches, and branches join into the trunk.
What Is the Mouth of a River?
The mouth of a river is the place where the river ends! It flows into something bigger, like a lake or the ocean.
How Does a River Get Bigger as It Travels?
A river grows as it goes, because more water keeps joining it! Tributaries pour in, rain runs off the land, and underground water seeps into the channel.
Why Do Mountain Streams Look So Fast and Big Rivers Look So Slow?
Mountain streams look fast because they tumble down steep slopes over rocks! Big rivers flow across gentle land, so their surface looks smooth and calm.
Which Rivers Are the Longest in the World?
The longest rivers in the world stretch for thousands of miles! The Nile in Africa and the Amazon in South America are usually named the two longest, each about 4,000 miles.
Are Brooks, Creeks, and Rivers Different Things?
Brooks, creeks, and rivers are all moving water, but there is no perfect rule for the names! In general, brooks and creeks are small streams you might hop across.
Why Are River Valleys Shaped Like a V in the Mountains but Wide Near the Sea?
High in the hills, a river valley looks like the letter V! Near the sea it is wide and flat.
How Does a River Carry Rocks and Sand Downstream?
A river moves material in three different ways! Tiny bits float, sand hops along the bottom, and big stones roll or slide.
Why Do Rivers Drop Sand and Pebbles When They Slow Down?
Moving water has energy, and fast water can carry heavy things! When a river slows down, it loses energy and can no longer hold its load.
What Is a Watershed?
A watershed is all the land that drains into one river! Every raindrop that lands inside it, on a roof, a field, or a hilltop, will eventually flow into the same stream or river.
Where Does All the Mud Go at the End of a River?
At a river's mouth, the current slows down and the mud and sand settle to the bottom! Over thousands of years, those layers pile up into new land called a delta.
What Happens Where a River Meets the Sea?
The place where a river meets the sea is called an estuary! Fresh river water mixes with salty seawater.
Why Does the Mackenzie River Run North Instead of South?
Rivers flow downhill, not toward the south! If the land slopes toward the north, the river runs north.
Why Do Some Rivers Split Into Many Weaving Channels?
Some rivers split into many weaving channels, like braided hair! They are called braided rivers.
Why Do People Argue About Where a River Really Starts?
A river often has many streams feeding it, so it can be hard to say which one is the real start! People pick the source in different ways.
How Old Are Rivers?
Rivers can be very old, or surprisingly young! Some have flowed in about the same place for millions of years.
Why Does a River Sometimes Leave an Old Loop Behind as a Crescent-Shaped Lake?
A winding river can leave an old loop behind as a crescent-shaped lake! It is called an oxbow lake.
Why Does River Water Turn White and Wild Over Rocks?
River water turns white over rocks because of millions of tiny air bubbles! Where a river drops steeply or runs over a bumpy bed, the water speeds up and tumbles.
Where Does a River’s Water Come From When It Hasn’t Rained for Days?
Many rivers are fed by groundwater, even when it hasn't rained for days! Groundwater soaks into the soil and rocks during rain and snowmelt.
Can a River Disappear Underground?
Yes, a river can disappear underground! In places with limestone rock, water can dissolve the rock and form holes and caves.
Why Do Some Rivers Have Different Names Along the Way?
People often name a river in separate parts, or give it different names along the way! A name is a human idea, but the water just keeps flowing.
Why Are River Rocks So Smooth and Round?
River rocks are smooth and round because they bump and rub together as the water carries them! Every bump knocks off tiny bits and rubs away sharp corners.
Where Does River Water Go After It Reaches the Sea?
River water goes back up into the sky after it reaches the sea! The Sun heats the ocean, and the water travels in a big circle called the water cycle.
How Can You Follow a Raindrop From Your Street to the Sea?
A raindrop that lands on your street takes a trip to the sea! It flows to the gutter, into a storm drain, and through pipes to a nearby creek or river.
How Can You Tell How Fast a River Is Moving?
You can find out how fast a river is moving with a leaf and a clock! Drop the leaf in at one point and time how long it drifts a measured distance.
Why Does Water Move Fastest in the Middle of a River?
Water moves fastest in the middle of a river because there is less rubbing there! The bottom and sides rub against rocks, mud, and plants.
Why Does a River Dig Deeper on the Outside of a Bend?
A river digs deeper on the outside of a bend because the water there flows faster! The faster water scrapes and wears away the bank.
What Are Riffles and Pools?
Along many streams, shallow bumpy stretches called riffles alternate with calm deep spots called pools! Riffles are noisy and bubbly, and they are great homes for insects.
Why Does a River Bottom Have Ripples Like Little Sand Dunes?
A river bottom has ripples, like little sand dunes, because moving water pushes sand along! Grains climb the back of a small hill and tumble down the front.
What Do Ripples and Smooth Patches on a River’s Surface Tell You?
A river's surface is like a map of the bottom! Smooth patches and ripples are clues about what is hiding below.
What Colors Can River Water Be, and What Do They Mean?
River water can be many colors, and each color is a clue! It can be brown with mud, green with algae, or clear over clean gravel.
Why Are Some Rivers Milky Turquoise?
Some rivers are milky turquoise because glaciers grind rock into a fine powder! The powder is called rock flour.
Why Do Some Rivers Look Dark Like Tea?
Some rivers look dark like tea because of natural stains from leaves and roots! The stains are called tannins.
Is a River as Deep as It Looks?
A river is not always as deep as it looks! Darker color and smooth surface can hint at depth, but you cannot be sure.
What Does a Stream Gauge Do?
A stream gauge is a station that measures how high the water in a river is, and how fast it flows! It sends the information by satellite or radio to scientists and to the public.
How Do Scientists Measure How Much Water a River Carries?
Scientists measure how much water a river carries by checking three things! They measure how wide the river is, how deep it is, and how fast the water moves.
Why Does River Temperature Change During the Day and Seasons?
River temperature changes during the day and across the seasons! Sunlight warms the surface, and shady banks and trees help keep water cool.
Why Do Some Rivers Have Foam on Top?
Some rivers have foam on top, and often it is completely natural! Leaves and plants release soap-like substances into the water.
What Is an Eddy?
An eddy is a patch of water that swirls in a circle or flows backward! It forms behind a rock, a bend, or some other obstacle.
Can Scientists Listen to Rocks Rolling Along a River Bed?
Yes, scientists can listen to rocks rolling along a river bed! They lower microphones called hydrophones, or place sensors on the bank.
What Can River Pebbles Tell Us About Upstream?
Each pebble in a river came from somewhere upstream! By looking at the kinds of rocks, scientists can tell which hills and mountains the river flows through.
What Do the Layers in a Riverbank Tell Us?
The layers in a riverbank are like pages in a book! A cut bank often shows stripes of sand, gravel, and mud.
What Is a Sandbar, and Why Does It Move?
A sandbar is a ridge of sand or gravel that builds up inside a river or near its mouth! It forms where the water slows and drops its load.
How Do Scientists Follow River Water with Harmless Dye?
Scientists sometimes release a safe, bright dye into a stream and watch how it travels! The dye shows how fast the water moves and how it mixes.
How Can You Read a River on a Map?
On a map, rivers appear as blue lines! Small blue lines join bigger ones, like branches on a tree.
What Is a Seam, Where Fast and Slow Currents Meet?
A seam is the line where a fast current meets slow, calm water! It often shows bubbles, foam, or little swirls.
How Do Whirling Pebbles Drill Holes in River Rock?
Whirling pebbles can drill round holes in hard river rock! The holes are called potholes.
Why Does a Wave Stay in One Place While the River Rushes Through It?
A river wave can stay in one place while the water rushes through it! It is called a standing wave.
How Do Scientists Map the Bottom of a River?
Scientists map the bottom of a river with sonar! Sonar sends a pulse of sound down and times how long the echo takes to return.
Why Do River Fish Face Upstream?
River fish usually point their noses into the current, which means they face upstream! Facing the flow helps them breathe, eat, and stay steady.
How Do Fish Hold Still in Fast Water?
Fish hold still in fast water by using smart body tricks and smart hiding spots! Smooth shapes, calm pockets, and strong fins all help.
What Lives Under the Rocks in a River?
Under river rocks live lots of tiny animals, like mayfly nymphs, stonefly nymphs, and caddisfly larvae! They are called water bugs, and they are important helpers.
How Do River Insects Breathe Underwater?
Many young river insects breathe underwater with gills, thin feathery parts that pull oxygen out of the water! Different insects wear their gills in different places.
Why Do Mayflies Live Only a Day as Adults?
Mayflies spend most of their lives underwater, then live as winged adults for only a short time! As adults, they do not eat at all.
How Do River Bugs Cling to Rocks in a Strong Current?
River bugs have clever grips, like flat bodies, claws, hooks, and sticky silk! These tricks keep them from being swept away.
Why Does Rushing Water Hold More Oxygen?
Oxygen from the air dissolves into water at the surface, and rushing water mixes in lots more! Tumbling over rocks splashes air into the stream.
How Do River Otters Stay Warm and Dry in the Water?
River otters have two layers of fur that trap air and keep water away from their skin! That air layer works like a cozy, waterproof jacket.
Why Do River Insects Let Go and Drift Downstream at Night?
After dark, many river insects let go of the rocks and float downstream. Scientists call it drift!
What Is a Dipper, the Bird That Walks Underwater?
The American dipper is a small gray songbird that walks underwater to find food! It lives beside fast mountain streams.
How Does a Kingfisher Dive for a Snack?
A belted kingfisher dives headfirst into the water to catch small fish! It is a champion fisher with a built-in spear.
How Do American Eels Swim From Rivers to the Faraway Sargasso Sea?
American eels grow up in rivers, then swim all the way to the Sargasso Sea to have babies! The Sargasso Sea is a part of the Atlantic Ocean near Bermuda.
Why Do Salmon Swim Up Rivers?
Many salmon hatch in a river, swim out to the ocean to grow, and then return to the river where they were born! They go home to lay their eggs.
How Do Young Fish Grow Up in a River?
Young fish grow up in safe nests and shelters, then slowly move to bigger water as they get strong! They hide, nibble tiny bugs, and grow.
Why Do Fish Leap Out of Rivers?
Fish jump out of rivers for lots of different reasons! Some are hunting, some are escaping, and some are traveling.
Can Dolphins Live in Fresh Water?
Yes! A few kinds of river dolphins live in big rivers in Asia and South America!
Why Do Frogs and Tadpoles Live in Quiet Corners of a River?
Frog eggs and tadpoles are soft and small, so they would be swept away in fast water! That is why they stay in calm corners.
How Can River Plants Bend Without Breaking?
River plants bend without breaking because they are flexible, and the water helps hold them up! They sway with the current instead of fighting it.
How Do Trees Along a Riverbank Help the Animals in the Water?
Trees along a riverbank are green helpers that take care of the animals in the water! They give shade, food, and shelter to fish, insects, frogs, and birds.
How Does a River Feed the Animals Along Its Banks?
A river is like a food highway that feeds animals along its banks! Fish, insects, and plants bring in hungry visitors.
Why Are Fallen Trees Good for a River?
A tree that falls into a river becomes a home for lots of animals! It makes shelter and food, and it changes the flow of the water.
Which Animals Wake Up Along a River at Night?
When the Sun sets, a whole new crew wakes up along the river! Bats, owls, raccoons, muskrats, and frogs all get busy, and fireflies may blink too.
What Are Freshwater Mussels Doing on the Riverbed?
Freshwater mussels sit half buried in the sand, pulling in water and filtering out tiny bits of food! They work like living water filters, cleaning the river as they feed.
Why Do Sturgeon Look Like Dinosaurs?
Sturgeon look like dinosaurs because they are very ancient fish that have changed little for millions of years! They have bony plates instead of scales.
How Do Animals Cross a Rushing River?
Animals cross rivers in many clever ways, but they choose their crossing spots carefully! Some swim, some fly, and some float, and some even team up.
Why Did People Build Towns Next to Rivers?
People built towns next to rivers because rivers give so much! They supply water, food, rich soil, and a way to travel.
How Did Rivers Become Highways?
Before roads and railways, rivers were the highways, and travelers floated or paddled along them! Boats could carry heavy loads easily, which made rivers the best roads.
Why Were Birchbark Canoes So Clever?
Indigenous peoples of northern North America built light, strong canoes from birch bark, cedar wood, and spruce roots! They sealed them with spruce gum.
How Does a Paddle Move a Canoe Forward?
When you pull a paddle backward through the water, the canoe moves forward! You push the water, and the water pushes back.
Why Do Flat-Bottomed Boats Work Well in Shallow Rivers?
A flat-bottomed boat sits high in the water, so it needs less depth to float! That is perfect for shallow rivers.
How Can a Ferry Cross a River Without an Engine?
Some river ferries have no engine at all. The river itself pushes them across!
What Is a Ford, and Why Were Fords Important?
A ford is a shallow, firm place where people could cross a river on foot or by cart! Long ago, there were few bridges.
How Does a Canal Lock Lift a Boat Uphill?
A canal lock lifts a boat uphill using only water and gravity! It is a chamber with gates at both ends.
How Is a Canal Different From a River?
A river is a natural channel that formed on its own, but a canal is dug by people! A canal is made for boats.
How Did Boats Travel Upstream Before Engines?
Before engines, boaters traveled upstream with paddles, poles, sails, and ropes! It was slow and took lots of muscle, and a trip upstream could take weeks.
How Did Paddlewheel Steamboats Work?
A paddlewheel steamboat used hot steam to turn a giant wheel that pushed the boat along! It burned wood or coal to make steam.
How Can a Barge Carry So Much?
Barges are wide, flat boats that can carry a huge load because water holds them up! A tug boat pushes them along.
How Do River Pilots Avoid Hidden Sandbars?
River pilots avoid hidden sandbars with charts, markers, sound waves, and plenty of experience! A river keeps changing, so pilots need clues, because sand moves in the current.
How Does a Water Wheel Turn?
Flowing water pushes against paddles or buckets on a big wheel and makes it turn! The turning wheel can do useful work, like grinding grain or sawing wood.
How Did a Water Mill Grind Grain Into Flour?
A water mill used the turning of a water wheel to spin heavy millstones that crushed grain into flour! The river did the hard work, so people did not need to grind by hand.
How Does a Hydroelectric Dam Make Electricity?
A hydroelectric dam turns the power of falling water into electricity! Water flows through big pipes and spins a turbine.
What Are the Gates and Spillway on a Dam For?
A spillway and gates let a dam release extra water safely! That keeps the dam safe and the river steady.
How Do Fish Get Past a Dam?
Fish get past a dam using a fish ladder, which works like a staircase of water! Many fish must swim upstream to lay their eggs.
How Did Loggers Float Trees Down Rivers?
Long ago, workers floated trees down rivers in a big event called a log drive! Spring floods carried the logs to sawmills.
How Does a Life Jacket Keep You Afloat?
A life jacket keeps you afloat because it is filled with foam or air chambers that are lighter than water! It pushes up on your body.
How Can Ocean-Going Ships Sail Deep Inside a Continent?
Ocean-going ships can sail deep inside a continent using a system called the St. Lawrence Seaway!
What Is a River Port?
A river port is a place where ships and barges load and unload cargo on a river! It is like a bus station, but for boats.
How Did Early Explorers Map Rivers?
Early explorers mapped rivers by sketching as they traveled and using simple tools! They also learned from people who already knew the rivers.
What Is a Weir?
A weir is a low wall built across a river to raise the water level a little or to measure the flow! Water spills over the top.
Why Are Many River Towns Built Above the Water, Not Right at the Edge?
Many river towns are built above the water because rivers rise in spring and after storms! Higher ground stays dry, even when the river rises.
Why Do Rivers Rise Every Spring?
Rivers rise every spring because winter snow melts all at once! In cold places, snow piles up on the land and in the mountains all winter long.
Why Can a River Be High on a Sunny Day?
A river can be high on a sunny day because the rain fell far away! A storm in the mountains sends water downstream, and it takes time to travel.
How Do Forecasters Know a River Is About to Flood?
Forecasters know a river is about to flood by measuring rain, snow, and river height! They gather lots of clues and put them together in a computer.
What Does “Flood Stage” Mean?
Flood stage is the water level where a river starts to cause trouble! At that height, water begins to spill over the banks onto roads or near buildings.
Why Is the Land Near a River So Rich for Farming?
Land near a river is rich for farming because floods leave fresh soil behind! The flat land beside a river is called the floodplain.
What Is a Levee?
A levee is a long raised bank or wall built beside a river to hold the water in! Levees help protect farms and towns during high water.
Why Is Floodwater Stronger than It Looks?
Floodwater is stronger than it looks because moving water is very heavy! Even a small amount of fast water has a lot of pushing power.
Why Does Rain Run Off Pavement Faster than It Soaks Into Grass?
Rain runs off pavement faster than it soaks into grass because pavement cannot soak up water! Soil is full of tiny spaces that act like a sponge.
How Do Forests and Wetlands Slow Down a Rising River?
Forests and wetlands slow down a rising river because they work like sponges! They soak up rain and slow the water as it moves.
Why Do Rivers Get Smaller in Late Summer?
Rivers get smaller in late summer because the water coming in drops way down! The snow is gone, the soil is dry, and there has been less rain.
What Happens to River Animals When the Water Gets Low?
When river water gets low, animals find cooler, deeper spots to wait it out! Fish, insects, and frogs each have their own tricks.
How Can You See a Drought in a River?
You can see a drought in a river because the water gets low and rocks poke out! A drought is a long time with much less rain and snow than normal.
What Can a Dry Riverbed Tell Us?
A dry riverbed tells us where water once flowed! Even without water, the shape of the land holds clues about the river.
Why Do Rivers Freeze Later than Ponds and Lakes?
Rivers freeze later than ponds and lakes because moving water is hard to freeze! Flowing, churning water keeps mixing and breaks up any ice trying to form.
Why Does Ice Grow Out From the Riverbank First?
Ice grows out from the riverbank first because the edges are slow, shallow, and cold! The fast, deep middle keeps flowing, so it stays open longer.
What Is Frazil Ice?
Frazil ice is a river slush made of tiny ice crystals! On very cold nights, rushing water can cool slightly below freezing.
Can Ice Grow on the Bottom of a River?
Yes, ice can grow on the bottom of a river! It is called anchor ice.
Why Does River Ice Boom and Groan?
River ice booms and groans because it is stretching and squeezing! Ice shrinks when it gets colder and expands when it warms.
How Can Ice Pile Up and Block a River in Spring?
Ice can pile up and block a river in spring when broken ice gets stuck! The pile acts like a dam made of ice.
What Is Spring Breakup on a Northern River?
Spring breakup is when the ice on a northern river breaks apart and moves! It is the end of the frozen winter and the start of open water.
Why Is River Ice Never Safe to Walk On?
River ice is never safe to walk on because it can be thin without any warning! Moving water wears the ice away from underneath.
How Do Fish Survive Under River Ice?
Fish survive under river ice because the water below stays liquid! The ice on top acts like a lid that keeps the water underneath from freezing solid.
Can the Ocean Push a River Backward?
Yes, the ocean can push a river backward, near the coast! When the tide comes in, the sea pushes up into the river mouth.
What Does a Flood Leave Behind?
After a flood, the river leaves behind mud, sand, logs, and sometimes a new channel! When the water goes down, you can see the story of what happened.
How Can Scientists Tell How Big a Flood Was Long Ago?
Scientists can tell how big a flood was long ago by reading clues in nature! Floods leave marks on trees, cliffs, and the land.
What Makes a River Healthy?
A healthy river has clean, cool water and lots of life! Its banks have plants and trees, and its bed has gravel and rocks.
Why Does a Clean River Have Lots of Different Bugs?
A clean river has lots of different bugs because many river bugs need clean water! Some can only live in cool water with lots of oxygen.
How Do Scientists Tell How Cloudy a River Is?
Scientists tell how cloudy a river is by measuring how much light gets through! Cloudy water is called turbid, and the cloudiness is called turbidity.
Why Does a River Need Oxygen?
A river needs oxygen because fish, insects, and other river animals breathe it! The oxygen is dissolved in the water, mixed in invisibly.
What Does a Water Test Kit Check?
A water test kit checks how healthy water is, using simple tests! It can measure pH, nutrients, and temperature, all in just a few minutes.
What Makes Green Slime Grow in a River?
Green slime grows in a river when algae get warm sunshine and extra nutrients! Algae are tiny plant-like living things that live in water.
How Do Detectives Find Where Pollution Is Entering a River?
Detectives find where pollution enters a river by testing the water at many spots! They compare clean water upstream with water farther downstream.
How Does Litter Travel Down a River?
A river carries whatever falls into it, and that includes litter! Bottles, bags, and cans float or roll along with the current.
How Can a Water Wheel with Googly Eyes Clean a River?
Mr. Trash Wheel is a floating machine with big googly eyes that cleans a river!
How Can a Strip of Plants Catch Muddy Runoff Before It Reaches the River?
A strip of plants along a river catches muddy runoff before it reaches the water! It is called a buffer, and it works like nature's filter.
How Do Scientists Bring the Wiggles Back to a Straightened River?
Scientists bring the wiggles back to a straightened river by rebuilding its natural bends! A straight channel is a poor home for fish and bugs.
How Do Scientists Count Fish They Can’t See?
Scientists count fish they can't see with gentle tools like cameras, sound, and tiny tags! The goal is to learn how many fish live in a river.
How Can a Cup of River Water Tell Who Lives There?
A cup of river water can tell who lives there because animals leave tiny traces of themselves! These traces are called eDNA, short for environmental DNA.
How Do Satellites and Drones Watch a Whole River at Once?
Satellites and drones watch a whole river at once by taking pictures from above! Satellites see the big picture from far above in space.
How Do Sensors Keep Watch on a River Day and Night?
Sensors keep watch on a river day and night by measuring it all the time! They never get tired or need to sleep, and they work in all kinds of weather.
How Do Floating Trackers Show Where River Water Goes?
Floating trackers show where river water goes by drifting along with it! They carry GPS, which sends their location to a screen.
How Can Kids Help Look After a River?
Kids can help look after a river in lots of safe ways! Small jobs on land protect the water downstream.
What Jobs Do People Do with Rivers?
Many people work with rivers, and each job is different! Some measure water, some study animals, and some design big machines.
How Can Old Maps Show That a River Has Moved?
Old maps can show that a river has moved by comparing where it used to flow! Rivers change their paths over decades.
What Is a Rain Garden?
A rain garden is a shallow, planted dip in the ground that collects rain! Instead of rushing into a storm drain, the water soaks in slowly.
How Do Experienced Boaters Decide Whether a River Is Safe to Paddle?
Experienced boaters decide a river is safe to paddle by checking lots of things first! They check before they ever touch the water, and they never paddle alone.
How Does a River Help Clean Itself?
A river helps clean itself with built-in helpers! Sunlight, rapids, tiny microbes, bugs, mussels, and plants all pitch in.
Are There Rivers on Other Worlds?
Yes, there are rivers on other worlds, and some used to flow with water! Long ago, Mars had rivers, and scientists are exploring the clues.
How Can You Safely Explore a River?
You can safely explore a river by watching from a safe spot with a grown-up! Looking, listening, and drawing are all great ways to learn about the river.
Which River Secrets Can Nobody Explain Yet?
Rivers still hold many secrets that nobody can explain yet! Scientists are still asking big questions about how rivers work, and some answers may take years.
From Book 1: The Great Expedition (2)
Why Do Rivers Flow to the Sea? Water Always Runs Downhill!
Rivers start small! Raindrops on a hillside trickle into tiny rills, rills join to become streams, and streams merge into rivers, all because water runs downhill.
Why Do Canyons Get So Deep? Rivers, Rock and Rising Land!
Canyons are amazing cuts in the land. Rivers start small, but over time moving water wears away rock and soil, and the land beneath can slowly lift upward, so the river carves even deeper.
From Book 2: The Inside Expedition (1)
From Book 3: The Built Expedition (1)
From Book 4: The Wild Expedition (12)
Why Do Beavers Build Dams?
A dam makes a beaver pond! Deep, still water hides the lodge door from land hunters.
Why Do Lakes Freeze From the Top?
Ice is lighter than liquid water, so it floats! Cold air nips the surface first, and the ice lid then covers the water below like a blanket.
Why Do Rivers Flow Downhill?
Gravity pulls water toward the lowest spot it can reach! A river is rain and melted snow sliding downhill in a channel, headed for a lake or the sea.
Why Do Ponds Get a Green Film in Summer?
That green film is often algae! Algae are tiny plant-like living things.
Why Does a Stream Make a Bubbling Sound?
Moving water slams into rocks and folds over itself! Air gets trapped in the water and pops.
Why Do Beavers Build Dams? Nature's Engineers
A dam is a beaver's tool for making deep, still water. Beavers are nature's engineers.
Why Do Wetlands Soak Up Floods?
A wetland is like a giant sponge. Water spreads out into shallow basins, and plants and spongy ground hold it.
Why Do Frogs Croak After Rain? The Pond Chorus
Rain makes travel and breeding easier for frogs. Wet ground does not dry out their skin, and puddles and ponds fill up.
Why Do Some Ponds Freeze While Springs Stay Open?
A still pond loses heat at its surface and can grow an ice lid. A spring has moving water that comes from underground.
Why Should You Not Drink Stream Water?
Clear water can still hide germs. You cannot see viruses or many bacteria, so pretty water is not always safe water.
Why Do Dragonflies Dart Over Ponds?
Dragonflies dart over ponds because a pond is their hunting ground! Ponds are full of tiny flying insects, and the water is where baby dragonflies grow up.
Why Is Pond Water Brown Sometimes?
Pond water turns brown when bits of nature get mixed into it! Soil washes in with the rain, and old leaves soak in the water like a tea bag.
From Book 5: The Time Expedition (5)
Follow the River! Why Do Old River Maps Help Fossil Hunters?
Rivers can carry and bury animals and plants in sand and mud. Maps of old river channels in rock can hint at where good fossil-hunting spots might be.
Ice Age Leftovers! Why Are Some Lakes Left by Ice?
During the ice ages, glaciers dug out hollows in the ground as they moved. When the ice melted, water filled many of those hollows and made lakes.
Deep Cuts! Why Do Canyons Get Deeper?
Water flowing through a canyon slowly wears away rock and carries bits of it downstream. Over a very long time, the river cuts deeper and deeper.
Wiggle Wiggle! Why Do Rivers Curve?
Water flows faster on the outside of a bend and wears away more of the bank there. On the inside of the bend, the water moves slower and drops sand and mud.
Backward Bound! Why Do Waterfalls Move Backward?
Falling water can wear away the softer rock under a waterfall's edge. When the rock above loses support, it breaks off.
From Book 6: The Ocean Expedition (3)
Why Do Currents Move Like Rivers in the Sea?
An ocean current is like a river with no banks. It's a huge stream of water that flows through the sea.
Why Is the Gulf Stream Famous?
The Gulf Stream is a strong, warm ocean current. It leaves the Gulf of Mexico, runs up the east coast of the United States, and then heads across the Atlantic toward Europe.
Why Does a Storm Surge Flood a Coast?
A storm surge is seawater pushed onto land by a storm's strong winds and low air pressure. It isn't just rain!
From Book 7: The Weather Expedition (3)
Why Is There Fog Near Lakes and Rivers?
Lakes and rivers keep adding invisible water vapor to the air above them. When cool night air settles over that moist air, the vapor can turn into tiny droplets.
Why Do Flash Floods Happen So Quickly?
A flash flood is a flood that arrives fast, with little warning. Very hard rain can fall faster than the ground and drains can soak it up, so the water has nowhere to go.
Why Do Jet Streams Race High Above Us?
Jet streams are fast rivers of wind high up in the sky. They blow about 9 to 12 kilometers above the ground, which is where airplanes cruise.
From Book 11: The Animal Expedition (2)
Why Do Beaver Families Build Together?
Beaver families build together because the work is big, and every beaver can help! Kits learn from their parents and older brothers and sisters.
Why Do Flamingos Stand in Shallow Lakes?
Flamingos stand in shallow lakes because that is where their food is! They filter tiny shrimp and algae from the water.
From Book 12: The Volcano Expedition (1)
From Book 13: The Light Expedition (2)
Why Does a Calm Lake Show a Mirror Picture and a Windy Lake Does Not?
Still water is flat, so it reflects light in an orderly way and makes a clear, upside-down picture. Wind and ripples tilt the surface into many little slopes.
Why Can a Pond Look Like a Mirror When You Look From Low Down?
When you look at water from low down, at a shallow angle, almost all of the light bounces off the surface like from a mirror. When you look from high above, more light passes through the water.
From Book 14: The Sound Expedition (3)
Why Do Voices Carry So Far Across a Calm Lake?
Voices carry far across a calm lake because the smooth water bounces sound instead of soaking it up! Cool air just above the water also bends sound back down.
Why Does a Frozen Lake Sometimes Make Strange Pew-Pew Sounds?
A frozen lake can make pew-pew sounds because cracking ice sends waves through the ice! High notes travel faster than low notes in ice.
Why Can You Hear a Clear Echo in a Canyon but Not in a Forest?
An echo is a sound that bounces off a hard surface and comes back to you! In a canyon, tall flat rock walls send your voice straight back.
From Book 16: The Desert Expedition (6)
Where Do Desert Animals Find Water If There Is No Pond?
Many desert animals get most of their water from their food! Seeds, insects, and juicy plants all hold water.
Why Are Some Desert Lakes Saltier than the Ocean?
Some desert lakes are saltier than the ocean because water can only leave them by evaporating! When the water evaporates, the salt stays behind.
Why Do Some Desert Rivers Vanish Into the Sand?
Some desert rivers vanish into the sand because they lose more water than they gain! Loose sand and gravel soak up the water, and the hot air makes the rest evaporate.
How Can a River Cross a Desert Without Drying Up?
A river can cross a desert without drying up if it starts where lots of rain or snow falls! These rivers are so big that the desert cannot use up their water quickly.
How Can a Lake Appear in the Desert After a Big Rain?
A lake can appear in the desert after a big rain because heavy rain fills dry basins with shallow water! These lakes are rare, and they do not last.
How Can Old Lake Shorelines Show Up on Desert Mountainsides?
Old lake shorelines show up on desert mountainsides because huge lakes once covered the land and then shrank! Waves carved level ledges into the mountains, like rings in a bathtub.
From Book 17: The Rainforest Expedition (3)
Why Do Some Rainforests Flood for Part of the Year?
In the Amazon basin, heavy rains and melting snow far away make rivers rise as much as 30 or 40 feet for months. The water spreads into the forest, creating a flooded forest.
What Are the Flying Rivers of the Amazon?
Flying rivers are streams of water vapor that flow through the air above the rainforest, carried by winds. They bring moisture from the Atlantic Ocean across the forest, and the trees add more along the way.
How Do Bromeliads Hold Tiny Ponds in the Treetops?
A bromeliad is a plant with leaves that form a cup, and the cup holds a tiny pond! Rainwater collects in the center, high up in the treetops.
From Book 18: The Polar Expedition (2)
From Book 20: The Mountain Expedition (2)
Why Would an Ibex Climb a Dam Wall?
An ibex climbs a dam wall to lick a salty snack! In Italy, a video showed Alpine ibex walking up a nearly vertical dam.
Why Do Mountain Streams Run Higher in the Late Afternoon?
Mountain streams run higher in the late afternoon because the Sun melts snow and ice all day. The meltwater takes time to flow down the slopes.
From Book 21: The Magnet Expedition (1)
From Book 23: The Flight Expedition (2)
From Book 24: The Underground Expedition (3)
How do builders make tunnels under rivers and seas?
One method is to dig a trench in the river bottom and sink tunnel sections built on land. The sections float like boats and then are lowered and joined in the trench.
Why is there a giant salt mine under Lake Huron?
About 400 million years ago, a shallow sea in this region dried up, leaving thick layers of salt that were later covered by rock. At Goderich, Ontario, workers dig this salt from about 1,800 feet below the ground, under the lake.
Why is gold found in streams?
Gold is very heavy, about 19 times heavier than water, and does not rust. When rock containing gold wears away, streams carry the pieces along.