The U.S. Fish and Wildlife Service (USFWS) has measured wetland losses for half a century and subsequently produced periodic Status and Trends studies on the nation's wetlands. These reports are based on a statistical sampling of the National Wetland Inventory (NWI) maps that focus on wetland acreage. In addition, the Environmental Protection Agency (EPA) is underway with a national wetlands condition assessment. States and tribes also conduct wetland assessments--and have developed a number of tools for assessment, such as Rapid Assessment Methods (RAM), criteria for determining functions, values, ecosystem services; and ecological integrity assessments, using biological indicators. Local governments and nonprofit organizations may employ similar and other wetland assessment methods specific to their locality.