Whether you live on the coast or in a land-locked state, odds are you’ve heard about wetlands. But how much do you know about wetlands really? In honor of American Wetlands Month, which occurs each May, we’re celebrating these vital ecosystems—starting with a crash course in Wetlands 101!

What are wetlands?

Fortunately, the name “wetlands” is pretty self-explanatory. Wetlands are areas of land that are periodically or constantly covered with water. Wetlands can either be tidal, meaning they contain sea water that fluctuates with tides, or non-tidal, meaning water presence is not linked to tides. The National Oceanic and Atmospheric Administration (NOAA) recognizes five types of wetlands: ocean, estuary, river, lake and marsh.

Depending on where you live, you may be familiar with one or many varieties of wetlands, like marshes (dominated by soft-stemmed plants), swamps (dominated by woody plants), bogs (freshwater zones with peat deposits and shrubs) and ferns (freshwater zones with peat deposits and grasses). Wetland type depends on a number of environmental factories, including soil type, water composition, plant type and frequency of water inundation.

Where are wetlands found?

Wetlands are found on every continent except Antarctica! It’s estimated 4-6% of land on Earth is actually wetlands. Wetlands comprise 5.5% of the continental United States, and about 95% percent of that is freshwater wetlands. Arguably the most well-known wetland system in the U.S. is the Everglades in Florida, which is currently preserved in the 1.5 million-acre Everglades National Park. Despite its size, the Everglades is only 50% of its original size—much of the Everglades has been drained for development in South Florida. Worldwide, other famous wetlands include the Okavango Delta in Botswana and the Mekong Delta in Vietnam.

Why are wetlands important?

 Wetlands provide countless environmental, cultural and economic services. First, they serve as critical habitat and nursery areas for fish, birds and other wildlife. Wetlands are often very nutrient-rich, which provides necessary food for animals at all levels of the food chain. They also absorb excess nutrients, including in the form of fertilizer runoff or septic leakage. This can help prevent those nutrients from flooding down into other habitats, like coral reefs. Additionally, they can help control erosion and reduce flooding in nearby areas: a study by the U.S. Army Corps of Engineers found that conserving wetlands near the Charles River in Boston avoided $17 million in future flood damage.

Why are wetlands in trouble?

Despite their importance to the ecosystem and economy alike, wetlands are at great risk worldwide. Drainage, dredging and diversion of wetlands interrupts the crucial ebb and flow of water that the ecosystems depend on. Pollution, including oil spills, can degrade the water quality and lead to die-offs of fish and birds. Increasingly, invasive plants and animals are changing the composition of wetlands by crowding out native species and altering the ecosystem structure. For example, nutria, an invasive rodent that is well established in wetlands in the United States Southeast, burrows into banks and eat massive amounts of native vegetation.

Want to learn more about wetlands near you? Check out this site to see wetlands in your state! And stay tuned as we celebrate wetlands all month long for American Wetlands Month!