Horicon Marsh, which encompasses both Horicon National Wildlife Refuge and Horicon Marsh State Wildlife Area, is the largest freshwater cattail marsh in the United States. Located in the largely agricultural landscape of southeast Wisconsin, Horicon Marsh is 32,000 acres of cattail marsh, open water, brush, and hardwood forest, with grassland, woodlots, and agriculture in the uplands.
Horicon Marsh is famous for its waterfowl, supporting huge numbers during migration, including some 250,000 Canada geese and 100,000 ducks in the fall. Significant numbers of shorebirds also use Horicon as a migratory stopover. Horicon hosts the largest breeding population of redhead east of the Mississippi River. It also supports significant breeding populations of waterbirds such as least bittern, American bittern, great blue heron, great egret, black-crowned night-heron, American white pelican, Forster’s tern, and black tern. Grassland habitat in the surrounding uplands supports some upland-nesting marsh birds such as mallard and blue-winged teal, as well as grassland birds like bobolink and dickcissel.