A swamp is an area of land permanently saturated, or filled, with water. Many swamps are even covered by water. There are two main types of swamps: freshwater swamps and saltwater swamps.

Swamps are dominated by trees. They are often named for the type of trees that grow in them, such as cypress swamps or hardwood swamps. Freshwater swamps are commonly found inland, while saltwater swamps are usually found along coastal areas. Swamps are transition areas. They are neither totally land nor totally water.

Swamps exist in many kinds of climates and on every continent except Antarctica. They vary in size from isolated prairie potholes to huge coastal salt marshes. Some swamps are flooded woodlands. Some are former lakes or ponds overtaken by trees and shrubs.

Freshwater Swamps

Freshwater swamps form around lakes and streams. Rain and seasonal flooding cause water levels to fluctuate. In the wet soil, water-tolerant vegetation grows and helps maintain a moist, swampy condition.

In many freshwater swamps in the southeastern United States, cypress and tupelo trees grow. Spanish moss may hang from the branches, and tiny plants called duckweed may cover the waters surface. Shrubs and bushes may grow beneath the trees. Sometimes poking as much as 4 meters (13 feet) above the water are angular knobs called cypress knees. They are outgrowths of the trees' root systems.

Alligators, frogs, and many other animals live in these swamps. These animals are adapted to fluctuating water levels. The shadowy tree root system and cypress knobs provide a rich, sheltered habitat for nesting birds, as well as fish, amphibians and reptiles.

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 abundant wildlife, agricultural opportunities, and ability for communication and trade fostered human technological development. The Fertile Crescent is recognized as the birthplace of civilization and the site of the first cities. The earliest recorded written language and the first recorded use of the wheel occurred around these swamps.

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. The Everglades is 97 kilometers (60 miles) wide and 160 kilometers (100 miles) long. A rich collection of wildlife, from alligators to panthers, calls this freshwater swamp home.

Saltwater Swamps

Saltwater swamps form on tropical coastlines. Formation of these swamps begins with bare flats of mud and sand that are thinly covered by seawater during high tides. Plants that are able to tolerate tidal flooding, such as mangrove trees, begin to grow and soon form thickets of roots and branches. Mangrove trees often grow on tall, thin roots. The roots anchor sand and other sediments. The growth and decay of the roots increase the accumulation of soil.

Among these mangroves live animals that feed on fallen leaves and other material. Crabs, conchs, and other shellfish are abundant in mangrove swamps. The swamps are also home to a huge variety of birds, whose droppings help fertilize the swamp.

Because the young of many marine animals find food and shelter in saltwater swamps, these wetlands are sometimes called the nurseries of the ocean. Many ocean species enter coastal wetlands to spawn. Fish swim into salt marshes to lay their eggs. When the eggs hatch, the young find plenty of food and some protection in swamp grasses or among tree roots. Other species spawn in the ocean, and the young swim into the wetlands and live there until they mature.

People and swamps

Swamps are among the most valuable ecosystems on Earth. They act like giant sponges or reservoirs. When heavy rains cause flooding, swamps and other wetlands absorb excess water, moderating the effects of flooding. Swamps also protect coastal areas from storm surges that can wash away fragile coastline. Saltwater swamps and tidal salt marshes help anchor coastal soil and sand.

The swamp ecosystem also acts as a water treatment plant, filtering wastes and purifying water naturally. When excess nitrogen and other chemicals wash into swamps, plants there absorb and use the chemicals. Many of these chemicals come from human activities such as agriculture, where fertilizers use nitrogen and phosphorus. Factories, water treatment plants, and homes also contribute to runoff. Chemicals not absorbed by plants slowly sink to the bottom and are buried in sand and sediment.

For most of history, wetlands were looked upon as wastelands, and as homes for insect pests such as mosquitoes. (Swamps are home to a wide variety of insects, which feed on the wide variety of plants.) People thought swamps were sinister and forbidding.

In the United States, filling or draining swamps was an accepted practice. Almost half of U.S. wetlands were destroyed before environmental protections were enacted during the 1970s. Most of the Everglades have been reclaimed as agricultural land, mostly sugar plantations. Draining swampland also created valuable real estate in the San Francisco Bay Area in California.

Federal and state authorities drained much of the wetlands at the delta of the Mississippi River in Louisiana as part of a massive system of river management. When Hurricane Katrina blew in from the Gulf of Mexico in 2005, the spongy swamp that traditionally protected the city of New Orleans from destructive weather patterns was diminished. The city was hit full force with a Category 3 hurricane.

Eradicating swampland also threatens economic activity. Two-thirds of the fish and shellfish that are commercially harvested worldwide are linked with wetlands. From Brazils varzeas, or freshwater swamps surrounding the Amazon River, to saltwater swamps near the Florida Keys, commercially valuable fish species that depend on wetlands are threatened with extinction.

In the early 1970s, governments began enacting laws recognizing the enormous value of swamps and other wetlands. In some parts of the United States, it is now against the law to alter or destroy swamps. Through management plans and stricter laws, people are trying to protect remaining swamps and to re-create them in areas where they have been destroyed.