Beaver Dam Lake spans 1,163 acres in Barron County, Wisconsin, with portions extending into the Towns of Maple Plain, Crystal Lake, and Cumberland. The lake is separated into distinct west and east basins, with downtown Cumberland situated between them. The West Lake basin is the larger of the two, featuring several named bays including Tiger Bay at the north end, Williams Bay west of Eagle Point, and Rabbit Island Bay. This western basin contains the lake's deepest point at approximately 106 feet at normal water level. The East Lake basin includes Norwegian Bay at the north end, City Bay east of downtown Cumberland, and Cemetery Bay south of Highway 48. This basin is predominantly open water with several smaller unnamed bays supporting extensive aquatic vegetation communities.

The two basins connect via a channel underneath the recently reconstructed Highway 63 bridge, which now allows for improved navigation between sections. Six public boat launches provide access around the lake, including Eagle Point Campground and Tourist Park.

The lake's maximum depth of 106 feet makes it one of the deeper inland lakes in the region, though water clarity varies significantly between basins. West Lake generally exhibits better water quality with mesotrophic to oligotrophic conditions, while East Lake tends toward eutrophic states, particularly in Norwegian Bay, which receives inflow from a 1937 diversion ditch that more than doubled the lake's natural drainage area.

The shoreline is almost entirely developed with residential properties, though some undeveloped stretches remain in west Rabbit Island Bay and along the north side of East Lake. Anglers target multiple species including muskellunge, northern pike, walleye, largemouth and smallmouth bass, and various panfish.

The lake's name reflects its history, as downtown Cumberland was once known as the "Island City" when surrounded by Beaver Dam, Library, and Collingwood Lakes before gradual infilling connected the roads. Water quality monitoring continues at multiple stations, with ongoing management addressing sediment loading and aquatic plant growth through various watershed improvement initiatives.