During the last four decades, several definitions of the term "wetland" have been offered by different sources. Today's legal and jurisdictional delineations were published in the Corps of Engineers Wetlands Delineation Manual and revised in 1989. It states that wetlands are "those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under usual circumstances support a prevalence of vegetation typically adapted for life in saturated soil conditions."

For an area to be a wetland, it must have certain hydrology, soils, and vegetation. Vegetation is dominated by species tolerant of saturated soil conditions. They exhibit a variety of adaptations that allow them to grow, compete, and reproduce in standing water or waterlogged soils lacking oxygen. Soils are wet or have developed under permanent or periodic saturation. The hydrologic cycle produces anaerobic soils, excluding a strictly upland plant community...