What If? Lab
What if there were no wetlands?
Wetlands are soggy places like marshes and swamps. They soak up rain, clean water and give birds a home. What if there were none? Let's imagine it with Olly!
Marshes, swamps and bogs are wetlands: places where water covers the soil or sits just below it. EPA compares them to natural sponges that soak up rain and floodwater and let it go slowly. They also clean water and shelter many birds and young fish. Imagine a world with no wetlands, and follow what might change.
Wetlands store and slowly release floodwater, retain nitrogen and phosphorus, trap sediment and support a large share of threatened species (EPA). UNEP reports that some 85 percent of the wetlands present in 1700 had been lost by 2000. This thought experiment reasons about what might change without them, and what people do to protect and restore them.
The big question
A wetland is a place where the ground is wet for much of the year.
Marshes, swamps and bogs are wetlands. What if there were none at all?
A wetland is a place where water covers the soil, or sits at or near the surface, for all or part of the year. Marshes, swamps and bogs are all wetlands. Some are by the sea, where salt water mixes with fresh water. Others are inland, along rivers, lakes and ponds.
What if every wetland disappeared? In this thought experiment you can follow three paths: what happens to floodwater, what happens to clean water, and what happens to the birds and fish that live there.
EPA defines wetlands as areas where water covers the soil, or is present at or near the surface, all year or for varying periods, including during the growing season. That saturation shapes their soils (hydric soils) and their specially adapted plants (hydrophytes). EPA groups them as coastal or tidal wetlands, linked to estuaries, and inland or non-tidal wetlands, such as riverside (riparian) wetlands, potholes, vernal pools and bogs.
This thought experiment removes wetlands and asks what might change for flood storage, water quality and habitat. It reasons from the functions EPA and UNEP describe; it does not model any one watershed.
Explore the idea
Make a prediction
When heavy rain falls, what is a wetland like?
During heavy rain, what does a wetland act like?
EPA compares a wetland's role in storing and releasing floodwater to…
- A sponge
- A drain pipe
- A mirror
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Established fact
Wetlands soak up water, clean it and give animals homes.
Wetlands store floodwater, improve water quality and provide homes for fish and wildlife (EPA).
Wetlands store and slowly release floodwater, retain nutrients and sediment, and support many threatened species (EPA).
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Established fact
Many wetlands have been lost, and people work to bring them back.
Some 85 percent of the wetlands of 1700 were lost by 2000 (UNEP), and countries work together to protect them.
UNEP reports 85 percent loss of 1700's wetlands by 2000; the 1971 Convention on Wetlands coordinates protection.
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An idea scientists discuss
A world with no wetlands is pretend. We imagine what might happen.
What might happen with no wetlands at all is an idea built from what wetlands do today.
Every consequence of a wetland-free world here is reasoned from present functions and might differ greatly in reality.
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Established fact
Wetlands are on every continent except Antarctica.
Wetlands are places where water covers the soil or sits near the surface for all or part of the year. They are found on every continent except Antarctica.
Wetlands occur from the tundra to the tropics on every continent except Antarctica; saturation shapes their hydric soils and hydrophytic plants (EPA).
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Established fact
Wetlands soak up water like a sponge and let it out slowly.
Wetlands work like natural sponges: they trap rain, snowmelt and floodwater and release it slowly, and their plants slow moving water down.
Wetlands trap and slowly release surface water, rain, snowmelt, groundwater and floodwater; vegetation slows flows, lowering flood peaks and reducing erosion (EPA).
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Established fact
Wetlands by one big river now hold much less water than before.
Wetlands along the Mississippi River once stored at least 60 days of floodwater. Now they store only 12 days, because most were filled or drained.
Bottomland hardwood riparian wetlands along the Mississippi once stored at least 60 days of floodwater; most have been filled or drained, and they now store 12 days (EPA).
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An idea scientists discuss
Without wetlands, rain might rush into rivers faster.
Without wetlands, rain and snowmelt might rush into rivers faster, and rivers downstream might rise higher after storms.
Removing all wetland storage might shorten the time runoff takes to reach channels and raise peak flows; the size of the effect might vary greatly between watersheds.
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Established fact
Wetlands help clean water by trapping mud.
As runoff passes through wetlands, they hold on to extra nitrogen and phosphorus, break down some pollutants and trap mud before it reaches open water.
Wetlands intercept runoff, retain or process excess N and P, decompose organic pollutants and trap suspended sediments that might otherwise clog waterways (EPA).
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Established fact
A big swamp cleaned as much pollution out of water as a water-cleaning plant.
A 1990 study found the Congaree Bottomland Hardwood Swamp in South Carolina removed as much pollution each year as a $5 million wastewater treatment plant.
A 1990 study found the Congaree swamp removed a pollutant load equivalent to that removed annually by a $5 million wastewater treatment plant (cited by EPA); EPA notes this capacity is not unlimited.
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An idea scientists discuss
Without wetlands, rivers might carry more mud.
Without wetlands, more mud and fertilizer might wash into rivers and lakes, and more algae might grow there.
Losing wetland retention might raise sediment and nutrient loads downstream, the conditions EPA links to algal blooms and dead zones; the size of the change cannot be estimated here.
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Established fact
Many birds feed, nest and raise their chicks in wetlands.
Ducks, geese, woodpeckers, hawks, wading birds and many songbirds feed, nest and raise their young in wetlands. Migrating waterfowl rest and feed there too.
Many U.S. breeding bird populations feed, nest and raise young in wetlands; migratory waterfowl use coastal and inland wetlands as resting, feeding, breeding or nesting grounds (EPA).
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Established fact
Many young fish grow up in coastal marshes.
Most commercial and game fish breed and raise their young in coastal marshes and estuaries. Shrimp, oysters, clams and crabs need these wetlands too.
Menhaden, flounder, sea trout, spot, croaker and striped bass depend on coastal wetlands; shrimp, oysters, clams and blue and Dungeness crabs need them for food, shelter and breeding (EPA).
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An idea scientists discuss
Without wetlands, some birds might need to find new places to rest.
Without wetlands, migrating birds might lose places to rest and feed, and many young fish might lose the marshes where they grow.
Species confined to wetlands, and migrants that depend on particular sites, might have no substitute habitat; which populations might cope cannot be judged here.
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Established fact
Countries made a promise to protect wetlands in 1971.
The Convention on Wetlands was adopted on 2 February 1971 in Ramsar, Iran. World Wetlands Day, every 2 February, marks that date.
World Wetlands Day marks the adoption of the Convention on Wetlands on 2 February 1971 in Ramsar, Iran; the 2023 theme was wetland restoration (UNEP).
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Established fact
Many wetlands have been drained, so people now work to save them.
Some 85 percent of the wetlands that existed in 1700 were lost by 2000, many drained for building and farming.
Some 85 percent of wetlands present in 1700 were lost by 2000, and wetlands are disappearing three times faster than forests (UNEP, 2022).
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Established fact
Saving wetlands can help keep towns safe from floods.
EPA says that preserving and restoring wetlands, along with other ways of holding water, can often control floods as well as expensive levees and dredging.
Preserving and restoring wetlands together with other water retention can often provide the flood control otherwise supplied by dredging and levees (EPA).
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An idea scientists discuss
If more wetlands come back, more birds might find homes.
If more wetlands are protected and restored, more of their sponge, cleaning and home-giving work might come back too.
Restoration might recover some functions, though a restored wetland might take many years to match an undisturbed one; that is beyond this experiment.
In our world
Wetlands are found on every continent except Antarctica.
Ducks, fish, beavers and alligators live in wetlands. People pick cranberries and wild rice there too!
Wetlands are found from the cold tundra to the tropics, on every continent except Antarctica. In the United States they include salt marshes along the coasts and mangrove swamps in southern Florida and Puerto Rico.
EPA calls wetlands "biological supermarkets" because they make so much food. Dead leaves and stems break down in the water into tiny bits called detritus, which feed small insects, shellfish and fish. Those animals are food for bigger fish, birds and mammals. People harvest fish, shellfish, blueberries, cranberries, timber and wild rice from wetlands.
EPA describes wetlands as among the most productive ecosystems in the world, comparable to rain forests and coral reefs. Shallow water, abundant nutrients and high primary productivity support a food web built on detritus: plant material broken down by bacteria, fungi and protozoa into nutrient-rich particles eaten by small invertebrates and fish.
They matter for biodiversity at a large scale. EPA notes that more than one-third of U.S. threatened and endangered species live only in wetlands and nearly half use them at some point. UNEP reports that over 140,000 described species, including 55 percent of all fishes, rely on freshwater habitats.
Imagine no wetlands
Let's pretend every wetland is gone.
Rain might rush away faster. Rivers might carry more mud. Some birds might need new places to rest. Let's find out why.
Now imagine every marsh, swamp and bog drained and dry. Rain and melting snow might rush straight into rivers instead of soaking in and trickling out slowly, so rivers downstream might rise faster after storms.
Muddy water might flow into lakes and the sea without being slowed and cleaned, and extra nutrients from fields might feed more algae. Ducks, wading birds and young fish that need wetlands might lose places to feed, nest and grow. These are ideas: we reason from what wetlands do today.
Without wetland storage, runoff might reach channels faster and in larger peaks, since EPA credits wetland storage and vegetation with lowering flood heights and reducing erosion. Losses of nutrient retention might raise nitrogen and phosphorus loads downstream, the conditions EPA links to algal blooms, dead zones and fish kills.
Habitat effects might be especially hard to replace: species that live only in wetlands, and migratory birds that depend on particular sites, have nowhere else to go. Carbon now held in wetland plants and peat might be released, because EPA notes that draining wetlands releases carbon dioxide. These are reasoned ideas, not predictions.
Why wetlands matter
Wetlands work like a giant sponge. They soak up rain and let it out slowly.
Wetland plants slow the water down. Then mud sinks, and the water gets cleaner.
EPA explains that wetlands act like natural sponges. They catch rain, snowmelt and floodwater and release it slowly. Trees, root mats and other plants slow the moving water and spread it out, which lowers flood heights.
Wetlands also clean water. As water passes through, wetlands hold on to extra nitrogen and phosphorus from fertilizer, break down some pollutants and trap mud before it reaches open water. A 1990 study found that the Congaree swamp in South Carolina removed as much pollution each year as a $5 million wastewater treatment plant.
Because they sit low in the landscape, wetlands store and slowly release surface water, rain, snowmelt, groundwater and floodwater; vegetation impedes flow, and the combined storage and braking lower flood peaks (EPA). Wetlands downstream of cities help counter the increased runoff from pavement and buildings.
For water quality, wetlands intercept runoff, retain or process excess nitrogen and phosphorus, decompose organic pollutants and trap suspended sediment. Anaerobic wetland soils host microbes that return nitrogen to the air as gas, and wetland plants take up phosphorus as they grow. EPA cautions that this capacity is not unlimited: too much polluted runoff can degrade wetlands.
Wetlands today
Many wetlands have been drained for farms and towns.
Now people around the world work to protect wetlands and bring them back. Every year, on 2 February, there is a World Wetlands Day!
People have drained many wetlands for building and farming. UNEP says some 85 percent of the wetlands that existed in 1700 were gone by 2000. Along the Mississippi River, EPA says riverside forest wetlands once stored at least 60 days of floodwater, but now store only 12 days, because most were filled or drained.
People are working to turn this around. In 1971, countries adopted the Convention on Wetlands in the city of Ramsar, Iran, and World Wetlands Day on 2 February marks that date. EPA says that protecting and restoring wetlands, along with other ways of holding water, can often control floods as well as expensive levees and dredging.
UNEP reports that some 85 percent of wetlands present in 1700 were lost by 2000, many drained for development and farming, and (in 2022) that wetlands are disappearing three times faster than forests. EPA gives a local example: Mississippi bottomland hardwood wetlands once stored at least 60 days of floodwater and now store only 12.
The Convention on Wetlands, adopted on 2 February 1971 in Ramsar, Iran, is marked each year by World Wetlands Day; its 2023 theme was wetland restoration (UNEP). EPA notes that preserving and restoring wetlands, with other water retention, can often provide flood control otherwise provided by dredging and levees. Built wetlands help too: a Baltic project uses floating, plant-rich wetlands to remove nitrogen and phosphorus from polluted lagoons (UNEP).
Amazing facts
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Beavers may even make their own wetlands!
Beavers may actually create their own wetlands, EPA says.
EPA notes that beavers may create their own wetlands, while species such as wood ducks, muskrat, cattails and swamp rose can live only in inland wetlands.
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People pick cranberries and wild rice from wetlands.
Fish, shellfish, blueberries, cranberries, timber and wild rice all come from wetlands.
Wetland products include fish and shellfish, blueberries, cranberries, timber and wild rice, and some medicines come from wetland soils and plants (EPA).
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Peat bogs hold lots of carbon.
Peatlands, a kind of wetland, store twice as much carbon as all the world's forests, UNEP says.
UNEP reports that peatlands alone store twice as much carbon as all the world's forests.
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Many black ducks spend the winter in Chesapeake Bay wetlands.
From 1950 to 1994, coastal wetlands in the Chesapeake Bay area supported an average of nearly 79,000 wintering black ducks each year.
Over 1950–1994, Chesapeake Bay coastal wetlands supported an annual average of nearly 79,000 wintering black ducks (EPA Watershed Academy).
Words to know
- wetland
- a place where water covers the soil or sits just below it for all or part of the year
- marsh
- a wetland where grasses and other soft-stemmed plants grow
- swamp
- a wetland where shrubs or trees grow
- estuary
- a place where a river meets the sea and fresh water mixes with salt water
- detritus
- tiny bits of broken-down dead plants that many small animals eat
- sediment
- mud, sand and other bits carried by water that can settle out
- restoration
- bringing a damaged place back toward health
Discovery challenge
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A wetland soaks up rain and lets it out slowly. What is it like?
EPA compares wetlands to what, because they soak up water and let it out slowly?
For their storage and slow release of floodwater, EPA likens wetlands to…
- Natural sponges
- Drain pipes
- Mirrors
Show the answer
Natural sponges
A sponge! It soaks up water and lets it out slowly.
Natural sponges that trap water and release it slowly.
…natural sponges that trap and slowly release water (EPA).
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Which continent has no wetlands?
Wetlands are found on every continent except one. Which one?
EPA notes wetlands occur on every continent except…
- Antarctica
- Africa
- South America
Show the answer
Antarctica
Antarctica, the icy continent.
Antarctica.
…Antarctica, from the tundra to the tropics everywhere else (EPA).
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When muddy water flows slowly through a wetland, what happens to much of the mud?
As runoff passes slowly through a wetland, what happens to much of the mud it carries?
What do wetlands do to suspended sediment in runoff?
- The wetland traps it
- The wetland makes more of it
- It turns into sand dunes
Show the answer
The wetland traps it
The wetland traps it, so the water gets cleaner.
The wetland traps it before it reaches open water.
They trap it, along with retaining nitrogen and phosphorus (EPA).
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How many days of floodwater could Mississippi River wetlands hold long ago, and now?
How many days of floodwater did Mississippi River wetlands store in the past, and how many now?
EPA's figures for Mississippi bottomland hardwood wetland flood storage, then and now, are…
- At least 60 days then, 12 days now
- 12 days then, 60 days now
- The same both times
Show the answer
At least 60 days then, 12 days now
At least 60 days long ago, but only 12 days now.
At least 60 days in the past, only 12 now, because most were filled or drained.
…at least 60 days once, 12 days now, after most were filled or drained (EPA).
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Why did countries agree to protect some wetlands?
Why was an international agreement made to protect certain wetlands?
EPA gives which reason for the international agreement on wetlands of international importance?
- Some migrating birds depend completely on them
- To build more roads on them
- To make them drier
Show the answer
Some migrating birds depend completely on them
Some birds need those wetlands to survive.
Some migrating birds depend completely on certain wetlands.
Some migratory bird species are completely dependent on certain wetlands (EPA).
Experiments to try
- Watch What If? Lab What if a river changed its course? A winding river wears away the outside of each bend and piles sand on the inside, so slowly, year by year, it moves. Sometimes it cuts off a loop and leaves a lake behind. Imagine a big river changing its course: what would happen to the old loops, and to the towns and bridges beside it?
- Watch What If? Lab What if a town used up its groundwater? Below the ground, water fills the tiny gaps between grains of rock and sand. In the United States, this groundwater is the drinking water for about half of all people. Rain and snow refill it, but often slowly. Imagine a town pumping faster than nature refills it, and follow what might change and how people help.
- Watch Try it What If? Lab What if beavers built no dams? Beavers eat willow and aspen, and they also build dams that turn streams into ponds. Take the beaver out of our forest food web and the model finds only one change. Then find out why scientists call beavers nature's engineers, and what a food web leaves out.
- Watch What If? Lab What if weather forecasts were always right? NOAA said in 2025 that a five-day weather forecast is right about 90 percent of the time, but a ten-day forecast is right only about half the time. Why? Because tiny changes in the air can grow into big differences, an idea called the butterfly effect. Imagine forecasts that were never wrong, and discover the satellites, balloons and supercomputers that make today's forecasts so good.
- Watch What If? Lab What if you found a meteorite? Meteorites are pieces of space rock that survived a fiery trip through Earth's air. Most come from asteroids, a few from the Moon or Mars, and many are older than any rock ever found on Earth. Imagine finding one: learn the clues scientists look for, what is inside, and why the right first step is to tell a grown-up and ask a museum or university.
- Watch What If? Lab What if mangroves lined every tropical coast? Mangroves are trees that grow where land meets the sea in warm places, standing on tangled roots. Their roots calm waves, give young fish a safe place to grow, and hold lots of carbon in the mud. Imagine mangroves along every tropical coast and follow three paths: calmer waves, fish nurseries and stored carbon, then find out where mangroves can and can't grow.
Explore next
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Watch
Animal
American flamingo
The American flamingo is a tall, bright pink wading bird of the Caribbean. It gets its color from pigments in the tiny water animals and algae it eats, and it feeds by filtering water through its bent bill with its head upside down. Flamingos live and nest in huge, noisy groups.
- Watch What If? Lab What if a river changed its course? A winding river wears away the outside of each bend and piles sand on the inside, so slowly, year by year, it moves. Sometimes it cuts off a loop and leaves a lake behind. Imagine a big river changing its course: what would happen to the old loops, and to the towns and bridges beside it?
- Watch What If? Lab What if a town used up its groundwater? Below the ground, water fills the tiny gaps between grains of rock and sand. In the United States, this groundwater is the drinking water for about half of all people. Rain and snow refill it, but often slowly. Imagine a town pumping faster than nature refills it, and follow what might change and how people help.
- Watch Try it What If? Lab What if beavers built no dams? Beavers eat willow and aspen, and they also build dams that turn streams into ponds. Take the beaver out of our forest food web and the model finds only one change. Then find out why scientists call beavers nature's engineers, and what a food web leaves out.
- Watch What If? Lab What if weather forecasts were always right? NOAA said in 2025 that a five-day weather forecast is right about 90 percent of the time, but a ten-day forecast is right only about half the time. Why? Because tiny changes in the air can grow into big differences, an idea called the butterfly effect. Imagine forecasts that were never wrong, and discover the satellites, balloons and supercomputers that make today's forecasts so good.
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Watch
Natural wonder
Pantanal
The Pantanal is one of the world's largest freshwater wetlands, mostly in Brazil and reaching into Bolivia and Paraguay. Each rainy season its rivers overflow and flood the lowlands, making shallow lakes and marshes; in the dry season the water slowly drains away. This rhythm feeds an amazing number of animals, from jaguars and giant otters to about 600 kinds of birds.
- Watch What If? Lab What if you found a meteorite? Meteorites are pieces of space rock that survived a fiery trip through Earth's air. Most come from asteroids, a few from the Moon or Mars, and many are older than any rock ever found on Earth. Imagine finding one: learn the clues scientists look for, what is inside, and why the right first step is to tell a grown-up and ask a museum or university.
- Watch What If? Lab What if mangroves lined every tropical coast? Mangroves are trees that grow where land meets the sea in warm places, standing on tangled roots. Their roots calm waves, give young fish a safe place to grow, and hold lots of carbon in the mud. Imagine mangroves along every tropical coast and follow three paths: calmer waves, fish nurseries and stored carbon, then find out where mangroves can and can't grow.
For parents & teachers
What children will learn
- Wetlands are places where water covers or saturates the soil for all or part of the year.
- Wetlands store floodwater, improve water quality and provide habitat for birds, fish and many threatened species.
- Many wetlands have been drained, and countries and communities work to protect and restore them.
- Thought experiments separate known facts from reasoned ideas.
Recommended ages: 7 to 17 · About 15 minutes
Talk about it
- Where is the nearest pond, marsh or creek to your home, and what lives there?
- Why might a town choose to restore a wetland instead of building a bigger drain?
- Why is it important to say that some of these outcomes are only ideas?
Try at home or in class
- Sponge test (EPA compares wetlands to natural sponges): tilt a baking tray on a book over a sink, pour a cup of water at the top and watch how fast it runs off. Then lay a damp kitchen sponge across the middle and pour again. How much water does the sponge hold back, and how slowly does it let it go?
- With a grown-up, visit a park pond, marsh or boardwalk, stay on the path, and count how many kinds of birds you see feeding or resting by the water.
Key vocabulary: wetland, marsh, swamp, estuary, detritus, sediment, restoration
Where these facts come from
- Why are Wetlands Important? , U.S. Environmental Protection Agency
- What is a Wetland? , U.S. Environmental Protection Agency
- Wetland Functions and Values (Watershed Academy Web) , U.S. Environmental Protection Agency
- Wetlands: the unsung heroes of the planet , UN Environment Programme
- World Wetlands Day 2023 , UN Environment Programme
Checked, not yet human-reviewed. Last updated October 24, 2026. Spotted a mistake? Tell us.