Reservoirs

The Wisconsin River Reservoir System consists of 21 water storage reservoirs used to regulate a uniform flow in the Wisconsin River. The reservoirs are located in Gogebic County in upper Michigan, and Vilas, Forest, Oneida, Lincoln, and Marathon counties in north central Wisconsin. They have a total maximum surface area of 61,265 acres. Reservoirs range in size from surface areas of 313 to 7,626 acres and from usable storage volumes of 23 to 4,170 million cubic feet. Total usable storage capacity of the reservoirs is 15,601 million cubic feet.

The WVIC reservoirs control runoff from 1,931 square miles of the headwaters region of the Wisconsin River basin, about one-sixth of the total basin area. As a result of the control of basin runoff, hydroelectric power generated on the river is increased by approximately 14 percent over what would be generated without control. Reservoir operation reduces flood flows, in some locations by as much as 30 percent.

In addition to supplementing hydroelectric generation and reducing flood flows, reservoir operation enhances the environment and the public's use of the Wisconsin River by increasing river flow during what would otherwise be naturally occurring periods of low flow. Reservoir operations can more than double flow during such periods. The man-made reservoirs add approximately 23,000 acres of water surface and 330 miles of shoreline, much of it in a wilderness state, to Wisconsin River valley recreation resources.

Natural-Lake Reservoirs

The system was initiated in 1907 and 1908 with the acquisition of 16 existing logging dams. These dams are all located at the outlets of natural lakes on streams that are tributary to the Wisconsin River, except for Lac Vieux Desert which is located at the outlet of a natural lake that is the origin of the Wisconsin River. The dams raised the levels of the associated natural lakes by several feet and were used in the late 1800s for transporting logs to downstream industrial facilities. This was done by storing water in the lakes and then opening the dam to cause a large artificial rise in river flow, generally at the same time natural flooding was already occurring, that would then float logs stored in the lakes to downstream markets. When WVIC acquired these dams the operation pattern was changed so that the storage and release of water from the lakes could be used to achieve more uniform downstream river flow. This operation is exactly opposite of that used for logging purposes. These reservoirs are known as natural-lake reservoirs.

Man-Made Reservoirs

From 1911 to 1937 WVIC constructed five new reservoirs, known as man-made reservoirs, to increase the capacity of the system. The five man-made reservoirs (Rainbow, Willow, Rice, Spirit, and Eau Pleine) have a larger range of allowable water level limits and hence much greater usable storage capacities than the natural-lake reservoirs. The five man-made reservoirs account for 73 percent of the system's total usable reservoir storage. The 16 natural-lake reservoirs account for the remaining 27 percent of the usable storage available in the system.