|Horicon National Wildlife Refuge|
IUCN category IV (habitat/species management area)
A boardwalk in the marsh
|Location||Dodge, Fond du Lac counties, Wisconsin, United States|
|Nearest city||Waupun, Wisconsin|
HORICON MARSH Latitude and Longitude:
|Area||21,400 acres (87 km2)|
|Governing body||U.S. Fish and Wildlife Service|
|Website||Horicon Marsh National Wildlife Refuge|
|Designated||12 April 1990|
|Reference no.||511 |
Horicon Marsh is a marsh located in northern Dodge and southern Fond du Lac counties of Wisconsin. It is the site of both a national and a state wildlife refuge. The silted-up glacial lake is the largest freshwater cattail marsh in the United States. 
Horicon Marsh was created by the Green Bay lobe of the Wisconsin glaciation during the Pleistocene era. The glacier, during its advance created many drumlins (a glacial landform) in the region, many of which have become the islands of Horicon Marsh. The marsh and surrounding Dodge County have the highest concentration of drumlins in the world.
During the glacier's retreat, a moraine was created, forming a natural dam holding back the waters from the melting glacier and forming Glacial Lake Horicon. The Rock River slowly eroded the moraine, and the lake drained. As the levels of silt, clay and peat accumulated in the former lake's basin, the Horicon Marsh was formed. Occasionally there have even been crop circles that appeared unexpectedly in several areas.
The Horicon Marsh State Wildlife Area is one of nine units of the Ice Age National Scientific Reserve system, being considered to contain unique, representative evidence of the Ice Age of the Pleistocene era. 
The Horicon Marsh area has been inhabited by humans, including the Paleo-Indians, the Hopewellian people and the Mound Builders, since the ending of the last Ice Age. Dozens of 1200-year-old effigy mounds were built by the Mound Builders in the surrounding low ridges.  Arrowheads have been found dating to 12,000 years ago. Later the region was inhabited by the Potawotomi, primarily to the east of the marsh, and the Ho-Chunk to the west. Seven well-traveled Native American foot trails met at the southern end of the marsh at the present location of Horicon.
When Europeans first arrived in the area, they named the marsh "The Great Marsh of the Winnebagos". The first permanent modern settlement along the marsh was the town of Horicon. In 1846, a dam was built to power the town's first sawmill. The dam held the water in the marsh, causing the water level to rise by nine feet. The "marsh" was called Lake Horicon, and was, at the time, called the largest man-made lake in the world.[ citation needed]
In 1869, the dam was torn down by order of the State Supreme Court, which ruled in favor of landowners whose land had been flooded.  The area became a marsh once more. In 1883, two sportsmen's clubs reported huge flocks of geese in the marsh, and stated that 500,000 ducks hatched annually, and 30,000 muskrats and mink were trapped in the southern half of the marsh.  Both birds and hunters flocked to the area, and the local duck population was devastated. From 1910 to 1914, an attempt was made to drain the marsh and convert it into farmland; these attempts failed, and afterwards the land was widely considered to be useless. 
In 1927, the Wisconsin State Legislature, after pressure from conservationists beginning in 1921, passed the Horicon Marsh Wildlife Refuge Bill, providing for the construction of a dam to raise the water to normal levels and for the acquisition of the land by the government. During the 1940s, the United States Fish and Wildlife Service bought the northern portions of the marsh.  Today the northern two-thirds, approximately 21,400 acres (87 km2), forms the Horicon National Wildlife Refuge. It is managed by the U.S. Fish and Wildlife Service.
Presently, the marsh is 32,000 acres (130 km2) in area, most of it open water and cattail marsh. The southern third, approximately 11,000 acres (45 km2), is owned by the state of Wisconsin and forms the Horicon Marsh State Wildlife Area, which was established as a nesting area for waterfowl and resting area for migratory birds. It is managed by the Wisconsin Department of Natural Resources (DNR). Millions of waterfowl, including over 200,000 Canada geese, migrate through the marsh. 
The refuges are habitats for many species of birds, especially ducks, great blue herons, and Canada geese (which have become increasingly common since the 1980s), as well as fish, frogs, snakes, turtles, muskrats, insects and plants.
- "Horicon Marsh". Ramsar Sites Information Service. Retrieved 25 April 2018.
- Will, Tracy (1997). Wisconsin. Oakland, California: Compass American Guides. p. 83. ISBN 1-878867-49-0.
- "Geology of Horicon Marsh". Wisconsin Department of Natural Resources. Retrieved April 26, 2018.,
- "Enjoy Horicon Marsh". EnjoyHoriconMarsh.com.
- Thomas E. Dahl; Gregory J. Allord (1996). History of Wetlands in the Conterminous United States (Report). United States Geological Survey Water Supply Paper, 2425. United States Geological Survey. ISBN 978-0-607-85696-5. Retrieved April 26, 2018.
- "Human history of Horicon: From wetland to wasteland and back". Wisconsin Department of Natural Resources. Retrieved April 26, 2018.
- About the Refuge. U.S. Fish and Wildlife Service. Accessed April 26, 2018.
- "The Annotated Ramsar List: United States of America" Archived 2013-09-04 at the Wayback Machine., "The Ramsar Convention of Wetlands", January 14, 2011, accessed February 22, 2011
- Facts About The Marsh Friends of Horicon Marsh
|Wikimedia Commons has media related to Horicon National Wildlife Refuge.|
- Horicon Marsh Wildlife Area - Wisconsin Department of Natural Resources
- Horicon National Wildlife Refuge - U.S. Fish and Wildlife Service
- Friends of Horicon Marsh Education and Visitor Center
- Enjoy Horicon Marsh - information about the Horicon Marsh and the communities that surround it
- The short film Horicon National Wildlife Refuge (2005) is available for free download at the Internet Archive