What is a Wetland?

A wetland is an area that is regularly saturated by surface water or groundwater and is characterized by a prevalence of vegetation that is adapted for life in saturated soil conditions (EPA, 1994).

From a regulatory standpoint, wetlands are defined by three criteria: hydrology, soils, and vegetation. The 1987 Corps of Engineers Wetlands Delineation Manual describes technical guidelines and methods to identify and delineate wetlands based on these three criteria. An area that meets all three criteria is considered a wetland for regulatory purposes (e.g., a “jurisdictional wetland”). The EPA and the Corps of Engineers use this manual to identify and delineate wetlands for the Clean Water Act Section 404 permit program, which regulates discharges of dredged or fill material into the waters of the United States, including wetlands.

In 2001, the scope of wetlands included in the definition “waters of the U.S.” was limited by a Supreme Court ruling, which found that certain isolated and non-navigable waters and wetlands are not subject to regulation under the Clean Water Act. This subject continues to be debated in the courts, and has enormous implications for the many thousands of miles of ephemeral and intermittent streams and acres of isolated wetlands across the country that may be at risk.

There are many different types of wetlands, including marshes, swamps, bogs, and fens, and almost as many different wetland classification systems. One commonly used system developed by Cowardin is described in Classification of Wetlands and Deepwater Habitats of the United States. The Cowardin system classifies wetlands based on landscape position, vegetation cover, and hydrologic regime. Major wetland types include marine, tidal, lacustrine, palustrine, and riverine. This system has been adopted by the U.S. Fish and Wildlife Service for use in the National Wetlands Inventory. This inventory produces and provides information on the characteristics, extent, and status of the Nation's wetlands and deepwater habitats.

Another commonly-used wetland classification system is the hydrogeomorphic (HGM) system described by Brinson in A Hydrogeomorphic Classification for Wetlands. The HGM system classifies wetlands based on their geomorphic setting, dominant water source (e.g., precipitation, groundwater, or surface flow), and hydrodynamics. Five major wetland types are defined by this system: riverine, slope, depressional, flat, and fringe.

Reference: Environmental Protection Agency (EPA). 1994. Report to Congress on the Great Lakes Ecosystem. US EPA. EPA 905-R-94-004. Washington, DC.