The formation and role of a wetland is driven by its location in the watershed, the presence of water during significant periods, soil quality and, ultimately, plants and animals. In fact, soils and plants act as "identifiers" for each wetland.

As sediment is deposited along river corridors, opportunistic plants and animals seek out the new habitat and flourish. As these areas mature, the soils change which impact the variety of plant and animal species. Thus new species may colonize. This process is called succession.

At the mouths of rivers sediments are often deposited forming alluvial plains. Marsh grasses find these areas desirable. In addition, other plants and many animals are then attracted to these deltas. Other wetlands are formed by aging lakes that fill-in with sediments. This area supports shrubs and trees adaptable to life in a wet environment.

Wetlands, once considered mosquito-infested, no man's lands with little economic or social value, are today often considered a saving grace of our planet. Over the past several decades, a better understanding of the ecology of wetlands and their invaluable benefits to all species and the environment has changed attitudes toward these diverse habitats.

Wetlands include swamps, marshes, bogs, ponds, river bottoms, sloughs, lakes, streams, potholes, and wet meadows to name just a few. Biologists categorize wet areas according to their formation, the types of vegetation they support, flooding pattern, water chemistry and soils. So many different wetland types and subtypes have been identified that it is simplest to look at broad categories of wetland systems and some of the wetland types that are included within the larger systems.

Ninety percent of the nation's wetlands belong to three categories that represent fresh-water systems. These include

1. Lacustrine: associated with lakes;
2. Riverine: habitats contained within channels such as rivers and streams;
3. Palustrine: meaning "marshy," including wet areas such as marshes, swamps and bogs.

Due to the abundant food supplies, vegetative cover, and water they contain, wetlands support a wide diversity of wildlife species. These areas provide a refuge for endangered and threatened species; important breeding, feeding, and migratory habitats for migrating waterfowl, shorebirds, and songbirds; and habitat for many water-loving wild animals including insects, reptiles, amphibians, crustaceans, and mammals. Wetlands, especially marshes adjacent to large bodies of water, also provide critical spawning and rearing habitat for fish.

Wetlands not only offer habitat for flora and fauna, but provide many socioeconomic services as well. Acting as giant natural sponges, wetlands absorb runoff from rain and melting snow and slowly release the stored water during drier periods, preventing flooding of rivers and streams. Dubbed "nature's kidneys," wetlands also provide natural purification systems by absorbing, filtering, and processing sediments, fertilizers and other pollutants, thereby improving water quality. By collecting sediment from surface runoff, wetlands reduce bank and soil erosion, and prevent silt from clogging rivers and filling lakes.

The role of wetlands, both natural and man-made, in improving water quality of streams, rivers, and lakes is illustrated with examples of fringe, instream, and riparian wetlands. Fringe wetlands have been shown to reduce inputs to freshwater lakes. Instream wetlands can improve habitat and provide some water quality function to small streams, and riparian wetlands along larger rivers provide important roles in both capturing sediments and nutrients from the river itself and serving as buffer between uplands and the river