Why Fishways are Used & How They Pass Fish
Large dams are among the most obvious and significant fish passage impediments. From a fish passage perspective, full dam removal is generally the preferred solution. Fishways allow fish and other aquatic life to bypass an existing dam and are typically utilized in situations where the dam owner has an interest in retaining the dam (e.g., recreational usage of the impoundment).
Fishways vary widely in size and type, depending on target species and unique site characteristics. Modern fishways generally adhere to the following criteria:
Ample pools and resting habitat
Channel length and width sufficient to minimize channel slope and provide surmountable flow velocities for target species
Fishway entrance near the face of the dam to provide attractant flows for migratory fish species
Weirs or "steps" throughout the channel, allowing for gradual ascension of the elevation change from downstream to upstream
In 2009, the Village of Thiensville and the City of Mequon began construction of a fishway in the former millrace of the Mequon-Thiensville Dam. Project partners included Ozaukee County, the U.S. Fish and Wildlife Service (USFWS), the Wisconsin Department of Natural Resources (WDNR), and others.
Goals of the Fishway
The fishway enables native fish and trout and salmon from Lake Michigan to migrate to spawning grounds and rearing habitats upstream of the dam. The project is expected to bolster fish populations and increase angling opportunities in the Milwaukee River Watershed and Lake Michigan.
The fishway is approximately 800 feet long and features a series of pools and riffles that allow fish to swim around the 6.5 foot high dam. Several dam safety concerns were also addressed during the project, including placing large rip rap along the downstream edge of the dam to break up the water “boil” and repairing the degraded “fish slide” and south abutment. Project partners also installed a pedestrian bridge, educational signage and the underwater camera to encourage public access and educational opportunities.