ASDSO Dam Safety Toolbox

Aquatic Life Movement

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Fish ladder at Bonneville Lock and Dam.

(Image Source: Wikipedia)

"Many dams in the Western United States are more than 75 years old and were constructed for irrigation, power generation, recreation, and flood control as part of the development of the Western United States. 'Human habitation in the West as we know it would not be possible witout this kind of active control and use of its surface water resource. Though vilified by many for the environmental damage they have caused, dams provide important, essential functions now relied upon to some degree by virtually every person who lives in the West' (MacDonnell, 1999). During early development, there was little information available about the life history requirements of resident and migratory fish species, and little consideration was given to their needs, especially in-stream migratory behavior. In many cases, dam construction has impeded fish movement and contributed to declining fish populations by limiting access to suitable spawning, rearing, and foraging habitat. Although significant attention has been given to understanding anadromous fish behavior and passage needs, very little attention has been given to other native fish. During the past 100 years, some 21 species and subspecies among 6 fish families have become extinct from the 17 Western States; some 64 species and subspecies are now Federally listed as threatened or endangered (Minckley and Deacon, 1992). Most of these species declines are related to alteration of habitat and the detrimental effects of non-native fishes. Recovery of threatened and endangered fish species requires reestablishing access to natural spawning, rearing, and forage areas."[1]

"Fish protection is an important aspect of fishery management at water diversions. Fish protection is often defined as fish exclusion from water diversions. Protection includes not only limiting entrainment of fish at diversions, but also protecting fish from injury or mortality resulting from operation of the diversion. The death and injury of fish at water diversions have long been identified as major sources of fish mortality (Spencer, 1928; Hallock, 1977). Fish entrained into agricultural or municipal and industrial diversions can experience nearly 100 percent mortality. Fish entrained into power intakes incur high mortality, and also experience injuries and disorientation that can lead to increased predation losses. A recent study on a seasonal irrigation canal associated with the Shoshone River in northwestern Wyoming provided insight into the potential for fish entrainment into these irrigation diversion systems. A total of 5,732 fish of 11 species were collected from a combined 5 miles of three canals by electro fishing, block netting, and draining techniques (Karp et al., 1993)."[1]

"Project regulation can influence fisheries both in the reservoir pool and downstream. One of the most readily observable influences of reservoir regulation is reservoir pool fluctuation. Periodic fluctuations in reservoir water levels present both problems and opportunities to the water control manager with regard to fishery management. The seasonal fluctuation that occurs at many flood control reservoirs, and the daily fluctuations that occur with hydropower operation often result in the elimination of shoreline vegetation and subsequent shoreline erosion, water quality degradation, and loss of habitat. Adverse impacts of water level fluctuations also include loss of shoreline shelter and physical disruption of spawning and nests."[2]

Best Practices Resources

Hydrologic Engineering Requirements for Reservoirs (EM 1110-2-1420), USACE


On-Demand Webinar: Introduction to Nature-Like Fishways for Dams


Revision ID: 7369
Revision Date: 07/21/2023