05/01/10; Minnesota, Wisconsin, Iowa and Illinois; 122,357 ha; 43°03'N 091°10'W. National Wildlife Refuges, National Monument. Natural floodplain backwaters of the Upper Mississippi River in the US Upper Midwest were enlarged and enhanced by construction of locks and dams in the 1930s to improve commercial and recreational navigation. Today the site consists primarily of flowing main and side channel habitats, large shallow to moderately deep backwater marshes, flooded floodplain forests and shrub-dominated communities. It is perhaps the most important corridor of fish and wildlife habitat remaining in the central US; e.g., it supports significant populations of over 100 native fish species and the nationally endangered Higgins' Eye Pearly Mussel (Lampsilis higginsii). In addition, the site is at the core of the Mississippi Flyway, through which 40% of North America's waterfowl migrate, e.g. Canvasback Ducks (Aythya valisineria) and Tundra Swans (Cygnus columbianus). Several federal and state-managed areas are located within the site and recreation is one of the major economic activities in the area (ca. 3 million visits each year). The site is currently threatened by the accelerating spread of plant and invertebrate invasive species. The Ramsar site includes the Upper Mississippi River National Wildlife and Fish Refuge, Trempealeau National Wildlife Refuge, and selected contiguous federal and state-managed floodplain wetlands associated with mouths of tributary rivers and streams. Ramsar site no. 1901. Most recent RIS information: 2010.