The marsh was formed by the retreat of the Green Bay Lobe of the Wisconsin Glacier roughly 12,000 years ago.
The refuge encompasses two distinct sections, with the northern two-thirds managed by the state and the southern third managed by the federal government.
It is a designated Ramsar Wetland of International Importance due to its role in supporting migratory bird populations.
The marsh acts as a natural water filtration system for the Rock River watershed.
During peak fall migration, the population of Canada geese at the refuge can exceed 200,000 birds.
The site hosts a significant breeding population of the state-endangered Forster's tern.
The peat layer beneath the marsh can be up to 10 feet thick in certain areas.
Horicon National Wildlife Refuge is the largest freshwater cattail marsh in the United States, covering 33,000 acres of open water, marsh, and upland habitat. It serves as a critical stopover point for massive flocks of migrating Canada geese and other waterfowl. The site is managed by the U.S. Fish and Wildlife Service to provide high-quality nesting and feeding grounds for wildlife. Visitors can access a network of hiking trails, observation blinds, and an auto tour route to observe diverse bird species. The refuge's ecology is defined by its glacial lake origins and sustained marshland vegetation. It is a prime destination for managed hunting, wildlife photography, and environmental education. The area features a dedicated visitor center with interactive exhibits regarding the local ecosystem. Wetland preservation efforts here have successfully restored populations of endangered species, including the trumpeter swan.
The Old Marsh Road auto tour pull-offs offer the most expansive views of the wetland for landscape and wildlife photography.
Bring binoculars or a spotting scope, as wildlife is often far from the trailheads.
Download or print the refuge map before arriving, as cellular service is intermittent in the marsh.
Check the refuge website for seasonal trail closures due to managed hunting activities.
Do not attempt to walk off-trail into the marsh, as the mud and deep water can be hazardous and ecologically destructive.
Select trails may close seasonally to accommodate waterfowl hunting seasons; visitor center hours vary by season.
Stay on marked trails to protect fragile nesting habitats; pack out all trash.
