At more than 33,000 acres, Horicon Marsh is one of the largest freshwater marshes in the United States and is a critical rest stop for thousands of migrating ducks and Canada geese. The northern two-thirds is managed by the U.S. Fish and Wildlife Service as the 22,000 acre Horicon National Wildlife Refuge. The southern third of the marsh, 11,000 acres, is managed by the Wisconsin Department of Natural Resources as Horicon Marsh State Wildlife Area. Three visitor centers and numerous trails and other outdoor facilities are available.

It is recognized as a Wetland of International Importance, as both Globally and State Important Bird Areas and is also a unit of the Ice Age Scientific Reserve. Horicon National Wildlife Refuge was established in 1941 to provide an undisturbed sanctuary for a number of migratory birds and waterfowl including the redhead duck as well as to provide opportunities for people to connect with nature.