Union Slough National Wildlife Refuge in northern Iowa was established in 1938 as a 3,334-acre haven and breeding ground for waterfowl and other migratory birds. On the eastern edge of the Northern Great Plains tallgrass prairie region, it protects wetland and prairie habitat in an area largely given over to corn and soybean farming. The slough is the remnant of a pre-glacial riverbed, and its name reflects the meeting of two watersheds linking the Blue Earth River in Minnesota with the East Fork of the Des Moines River. Its unusually flat terrain can even allow wind direction to influence water flow, making it a distinctive refuge for prairie and wetland wildlife.