What is a Wetland (Swamps, Marshes & Bogs etc) ?

Wetlands are areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season.

Wetlands are transition zones, they are neither totally dry land nor totally underwater; they have characteristics of both.

The water in wetlands is either freshwater, brackish or saltwater and may support both aquatic and terrestrial species.

The prolonged presence of water creates conditions that favor the growth of specially adapted plants (hydrophytes) and promote the development of characteristic wetland (hydric) soils.

Wetlands are found from the tundra to the tropics and on every continent except Antarctica.

With 35% wetlands lost globally since 1970, wetlands are the most threatened ecosystem and are disappearing three times faster than forests, according to the Global Wetland Outlook of Ramsar Convention.

Wetlands contribute a number of functions - water purification, groundwater replenishment, stabilization of shorelines and storm protection, water storage and flood control, processing of carbon and other nutrients and pollutants, and support of plants and animals.

The world's largest wetlands include the Amazon River basin, the West Siberian Plain, the Pantanal in South America, and the Sundarbans in the Ganges-Brahmaputra delta.

There are four main kinds of wetlands - marsh, swamp, bog and fen (bogs and fens being types of mires).

Some experts also recognize wet meadows and aquatic ecosystems as additional wetland types.

Sub-types include mangrove forest, carr, pocosin, floodplains, mire, vernal pool, sink, and many others.


A swamp is a wetland permanently saturated with water and dominated by trees.

Swamps are transition areas - they are neither totally land nor totally water.

There are two main types of swamps: freshwater swamps (inland) and saltwater swamps (coasts).

Freshwater swamps

Freshwater swamps often form on land around lakes or streams, where the water table is high and runoff is slow.

Water-tolerant plants, such as cattails, lotus, and cypress, grow in the swamp's wet soil.

Freshwater swamps are common in tropical areas near the Equator.

Tall evergreen trees such as bubinga and ovangkol dominate the swamp forests - the thick canopy of trees are more shaded and humid than other wetlands.

The muddy floor of these swamps is home to hundreds of insects, reptiles, and amphibians, including dozens of species of frogs.

The freshwater swamps between the Tigris and Euphrates Rivers in the Middle East are so rich in biodiversity that the area is called the "Fertile Crescent."

The Everglades, in Florida, is one of the largest swamp complexes in the United States.

Called the "River of Grass," this freshwater swamp is actually a wide, slow-moving river flowing from the Kissimmee River near Orlando to the Straits of Florida.

Saltwater Swamps

Saltwater Swamps begins with bare flats of mud or sand that are thinly covered by seawater during high tides, these swamps are usually found along tropical coastlines.

The brackish water of saltwater swamps is not entirely seawater, but not entirely freshwater, either.

Some hydrophytes, such as mangrove trees, can tolerate brackish water.

Many organisms live among mangrove roots i.e. crabs, conchs, and other shellfish.

Mangrove roots and branches provide excellent nesting sites for huge variety of birds - seabirds, such as gulls, as well as freshwater birds, such as herons.

The Sundarbans, a saltwater swamp in India and Bangladesh, has the largest mangrove forest in the world.

Insects such as bees build hives in the trees.

Storks, ibises, and herons nest in the high branches of mangrove and palm trees.

Many reptiles and amphibians live in and around the swamp, including frogs, toads, turtles, crocodiles and snakes.


Unlike swamps, which are dominated by trees, marshes are usually treeless and dominated by grasses and other herbaceous plants.

Herbaceous plants have no woody stem above ground, and they grow and die back on a regular cycle.

Marsh grasses and other herbaceous plants grow in the waterlogged but rich soil deposited by rivers.

These wetlands form a flat, grassy fringe near river mouths, in bays, and along coastlines.

Inland Freshwater Marshes

Inland freshwater marshes are found along the fringes of lakes and rivers where the water table, the upper surface of underground water, is very high.

They vary in size from bowl-shaped depressions called prairie potholes to the vast, watery grasslands of the Florida Everglades.

Prairie potholes are bowl-shaped depressions left by chunks of glacial ice buried in the soil during the most recent ice age. When the ice melted, muddy water filled the potholes.

Wet meadows do not support aquatic plants, plants establish seeds on a yearly basis, and only bloom with annual or biannual flooding of the meadow. Insects, especially butterflies, flourish in wet meadows.

Wet meadows: Wetland ecosystem that is saturated with water, but does not have standing water, for most of the year. The ecosystem supported by these primary consumers include frogs, snakes, and even apex predators such as bears.

The Everglades, the largest freshwater marsh in the United States, are drowned in a shallow layer of water all year.

The Everglades, also called "River of Grass" are rich in biodiversity and supports plants such as sawgrass, cypress, and mangrove forests.

Everglades are home to animals such as ducks, geese, raccoons, turtles, and frogs, predators such as alligators and panthers are also indigenous to the Everglades.

The Okavango Delta in Botswana (Africa) is probably the largest freshwater marsh in the world.

Okavango marshes are made up of dense beds of papyrus, water lilies, and underwater plants such as bladderworts.

The Okavango Delta is a haven for a diverse number of animal species, such as hippopotamuses, crocodiles, giraffes and elephants etc.

Tidal Marshes

Tidal salt marshes form a grassy fringe near river mouths, bays, and along coastlines protected from the open ocean.

Ocean tides fill the marsh with salty water and cause the water level to rise and fall twice a day; the marsh is deeper at high tide and shallower at low tide.

Plants such as sawgrass and pickleweed can tolerate fluctuating tidal waters, which are too salty for most trees and bushes.

Tidal freshwater marshes lie farther inland than salt marshes, but are close enough to the coast to be affected by tidal fluctuations.

Just like in salt marshes, the water level rises and falls twice every day, along with the tides.

Tidal freshwater marshes, however, are fed by freshwater streams and do not have a large salt content.

Tidal freshwater marshes are common boundaries between forests and rivers.

Herbaceous plants called sedges (water chestnut and papyrus) dominate the tidal freshwater marsh ecosystem.


A bog is a freshwater wetland of soft, spongy ground consisting mainly of partially decayed plant matter called peat.

Bogs are generally found in cool, northern climates.

They often develop in poorly draining lake (kettle lakes) basins created by glaciers during the most recent ice age.

Bogs are often called moors or fens in Europe, and muskegs in Canada.

The world's largest wetland is a series of bogs in the Siberia region of Russia.

All bogs take hundreds or thousands of years to develop.

A bog is formed when a lake slowly fills with plant debris.

Sphagnum moss, as well as other plants, grow out from the lake's edge, the vegetation eventually covers the lake's entire surface.

Eventually, watery bogs become choked with living and decaying plants. These slowly decaying plants become the main components of the bog's soggy soil, called histosol.

Thick, spongy layers of histosol eventually form peat.


A fen is bog-like peat-accumulating wetland fed by mineral-rich ground or surface water.

The unique water chemistry of fens is a result of the ground or surface water input.

Bogs and fens, both peat-forming ecosystems, are also known as mires.

The main difference between a fen and a bog is that fens have greater water exchange and are less acidic, so their soil and water are richer in nutrients.

Fens are often found near bogs and over time most fens become bogs.

Fens are dominated by sedges and mosses, particularly graminoids that may be rarely found elsewhere, such as the sedge species Carex exilis.

They also play important roles in the cycling of nutrients such as carbon, nitrogen, and phosphorus due to the lack of oxygen (anaerobic conditions) in waterlogged organic fen soils.