The Brule River sea lamprey barrier and fish ladder, Wisconsin

In the early 1950s, sea lampreys Petromyzon marinus devastated fisheries in the Great Lakes. Beginning in the late 1950s, chemical control reduced sea lamprey numbers, but the chemical has inherent drawbacks and its future use may be limited or restricted. In 1985, the Wisconsin Department of Natural Resources designed and installed a combination fish ladder and sea lamprey barrier at a low-head dam on a popular fishing stream in northwestern Wisconsin. This ladder-barrier combination allows free passage of salmonids but eliminates sea lampreys from the upper Brule River, which has been one of the largest producers of sea lampreys among the tributaries to western Lake Superior. Nearly 100% of sea lampreys migrating upstream are trapped and removed from the river before they spawn. However, unless sea lampreys continue to be attracted to the Brule, they may spawn elsewhere; the barrier may thus lose its effectiveness for control of sea lampreys in Lake Superior, and it could contribute to increased sea lamprey populations in other streams