The profile and an approximate outline of the flooded area for the regional (100-year) flood has been determined for a 21.3-mile reach of the Yahara River, Dane County, Wisconsin, from State Highway 113 at the head of Lake Mendota downstream to the dam at the outlet of Lake Kegonsa. The reach consists principally of lake surface, which results in large amounts of flood-storage volume. The regional-flood profile ranges from 1.7 feet to 3.1 feet above normal low-water elevation.