"The term 'wetlands' means those areas that are inundated or saturated by surface or ground water at a frequency and duration to support . . . a prevalence of vegetation typically adapted for life in saturated soil conditions." [33 CFR 328.3(b), 1984.] Wetland plant species that are common in Missouri include broad-leaved cattail, black willow, and water smartweed. Wetland ecosystems provide a variety of beneficial functions, such as habitat for endangered and threatened species, water quality improvement, and storage of stormwater runoff. Most of Missouri's original wetlands occurred within the floodplains of major rivers. A large percentage of these original natural wetlands have been drained and converted to agriculture or other human development. Section 404 of the Clean Water Act requires any activity that will affect wetlands to be reviewed by the Army Corps of Engineers and be authorized by a permit. The 404 permit is approved or denied depending on whether appropriate measures to avoid, minimize, or replace affected wetlands have been included in the project. In this manner, unnecessary detrimental effects on wetland resources are prohibited, but essential projects are approved if unavoidable losses of wetland functions are replaced elsewhere. This 'compensatory mitigation' occurs through the creation or restoration of wetland habitat. MoDOT is required by federal and state executive orders to ensure that projects cause no net loss of wetlands. MoDOT monitors all wetlands losses and gains from its projects to ensure compliance with those executive orders. MoDOT has a staff of highly trained wetland professionals who are responsible for determining the size and location of wetland impacts related to individual transportation projects. If impacts are unavoidable, the wetlands team develops practicable replacement wetland projects. An example of a MoDOT wetland replacement project is the restoration of Little Creve Coeur Lake in St. Louis County. This site is an old oxbow of the Missouri River, which had been pumped dry annually to allow for agricultural production. MoDOT purchased the oxbow, has allowed the natural fluctuation of water levels to resume, and will continue the restoration process by encouraging the development of native forest, grassland, and marsh plant communities.