Little Falls Dam to Get a New Fishway

by David Winer

Sycamore Islander, April 1999

The information and pictures in this report were extracted from a Web Site maintained by The Chesapeake Bay Program. Program partners include the states of Maryland, Pennsylvania and Virginia; the District of Columbia; the Chesapeake Bay Commission, a tri-state legislative body; the Environmental Protection Agency; and participating advisory groups.

Little Falls Dam on the Potomac River blocks anadromous fish like shad and herring from moving upstream in the spring to spawn. The dam blocks access to 10 miles (1,000 acres) of excellent fish spawning and nursery habitat, from Little Falls upstream to Great Falls. This area once supported an important recreational fishery for American shad and other migratory and resident fish species. Now, these species are almost non-existent in the upper reaches of the watershed due to man-made blockages on the tributaries. Virginia and Maryland have placed moratoriums on several of these species in an effort to reduce the fishing pressure, but the tributary spawning habitat still must be restored.

Little Falls Dam was built by the U.S. Army Corps of Engineers in 1959 as a water supply facility for the Washington area. Since the dam would block upstream fish movement, a vertical slot fishway was built at the same time at Snake Island near the center of the dam. Unfortunately, this fishway never passed migratory fish, mainly because its entrance is too far downstream from the dam, and its maintenance needs were too high due to the large amount of debris carried by the Potomac River. Its operation was abandoned in 1964.

The Maryland Department of Natural Resources designated a new fishway at Little Falls Dam as one of its highest priority fish passage projects in 1988. The innovative design uses three "W"-shaped labyrinth weirs within and below a 36-foot wide, 4-foot deep notch in the dam. The weirs reduce water velocity to levels that allow fish to move upstream over the passage despite a wide range of river flow.

Construction of the fishway is planned to start in summer 1999, so that it will be in place for the fish migration in spring 2000. The young shad that were raised and released starting in 1995 may start to return in 2000.