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DNR Dam Safety
DNR Dam Safety Program, WT/3
101 South Webster Street
PO BOX 7921
Madison, WI 53707–7921

Dams overview

With more than 15,000 lakes and 84,000 miles of rivers and streams, Wisconsin has an abundance of water resources. Many of these water bodies have water levels that are controlled by dams. A dam is a barrier that impounds water and generally serves the primary purpose of retaining water. Wisconsin law defines a dam as "any artificial barrier in or across a watercourse which has the primary purpose of impounding or diverting water and includes all appurtenant works, such as a dike, canal or powerhouse." (Wis. Admin. Code, Chapter NR 333).

Learn more about the history of dams in Wisconsin, their regulation, hydroelectric generation at dams, dam removal and answers to frequently asked questions about dams.

Important dam facts

Number of dams in the state There are approximately 3,900 dams currently in existence in Wisconsin. Since the late 19th century, approximately 900 dams have been built then washed out or removed.

Percentage of dams by ownership type: 60 percent of the dams in Wisconsin are owned a company or private individual, 9 percent by the State of Wisconsin, 17 percent by a municipality such as a township or county government, and 14 percent by other ownership types.

Jurisdiction The federal government has jurisdiction over most large dams in Wisconsin that produce hydroelectricity – approximately 5 percent or nearly 200 dams. The DNR regulates the most of the remaining dams in the state. Some dams or dam-like structures are not regulated by the state because they are not on a watercourse, impound a liquid substance other than water or are associated with a cranberry operation.

Large dam A dam is classified as a large dam if it has a structural height of over 6 feet and impounds 50 acre–feet or more, or has a structural height of 25 feet or more and impounds more than 15 acre–feet. There are approximately 1,160 large dams in Wisconsin. Because of their greater potential to impact downstream areas in the event of a failure, state regulated, large dams have mandatory inspection and design requirements

Hazard Ratings Hazard ratings are set for all large dams in the state. The "hazard" rating is not based on the physical attributes, quality or strength of the dam itself, but rather the potential for loss of life or property damage should the dam fail. A dam is assigned a rating of High Hazard when its failure would probably put lives at risk.

Last revised: Tuesday July 07 2015