During a 200-year period (1780 – 1980), US Fish and Wildlife Service and US Geological Survey inventories establish the contiguous United States experienced a 53% loss in wetlands, from 392 to 104 million acres and in the 11 states north of Chesapeake Bay, extent of wetland loss ranged from 9% (NH) to 74% (CT); exceeding 50% for four others (PA, DE, NY, and MD). USFWS inventories in 1997 indicate wetland loss during the preceding decade declined by 80%, to 290,000 acres per year. Between 2004 and 2009 however, although rate of wetland reestablishment increased, national wetland losses exceeded gains.

Sharing similar hydrologic, geomorphic, chemical or biological attributes, five broad wetland SYSTEMS are recognized - Marine, Estuarine, Riverine, Lacustrine and Palustrine. Long thought to be wastelands, attributes and/or physical processes used to differentiate wetlands also provide a variety of functions including wildlife habitat and those tied to the hydrologic cycle- groundwater recharge, flood control and water quality improvement. Recognizing not all wetlands perform all functions, nor do they perform all functions equally well, the US Environmental Protection Agency, US Army Corps of Engineers and others have developed functional assessments to identify and evaluate specific wetland functions.

Unavoidable wetland losses result from development essential to fundamental societal requirements including: airports, businesses, highways, hospitals, housing, schools and utility corridors Under nationally adopted policy referred to as “No Net Loss” implemented in 1989, federal permitting by Section 404 of the Clean Water Act and similar State permitting requires sequential implementation of mitigative measures, commencing with an evaluation of alternatives to not only avoid but minimize wetland loss. Appropriate compensatory mitigation, in the forms of creating new wetland, restoring previously filled or drained wetland, enhancing degraded wetland or preserving higher quality wetland, typically at ratios exceeding impact, is then implemented to offset unavoidable loss of wetlands. Legal instruments addressing ownership, management and sustainability are also necessary for long-term protection of compensatory mitigation.