Environmental Impacts of Dams

Protection and restoration of river environments is essential for sustainable, diverse, and productive stream fisheries. Over the last two decades, fisheries managers and ecologists have explored the changes dams cause in the ecological processes of river environments. Rivers emerging downstream of a dam may be substantially altered from the character of the river entering an impoundment above a dam. Aquatic community health is closely linked to water temperature tolerances and impounded waters may discharge at significantly higher or lower temperatures than normally encountered in the stream. Flow patterns reflecting normal high and low water conditions over time may also be fundamentally altered, affecting stream channel configuration, fisheries habitat, and many other physical and biological processes. Water quality may decline in impounded streams if excessive nutrients, sediments, and aquatic plants accumulate in the impoundment. Stream changes induced by dams and other watershed conditions are often reflected in the fish community. Native and desirable stream species are almost always displaced in river segments affected by dams. Dams also limit the normal movement of fish, other aquatic organisms, and system organic material.

The 103 hydroelectric facilities in Michigan impact 49 river systems, including almost every major river system in the state. These facilities, at a minimum, prevent anadromous fish movement into 2,063 mainstem river miles, dewater 57 river miles, directly impound 623 river miles, and impact 733 river miles through their operation. The total reservoir area impacted by these facilities is approximately 123,000 acres. These facilities produce, in net, only 1.5% of the electricity in the State of Michigan (Patric and Kakela 1983).

Patric, W. C., and P. J. Kakela. 1983. Small scale hydroelectric power in Michigan: A resource assessment. Michigan State University, Agricultural Experiment Station Research Report No. 442. 15pp.