The plus side to this type of dam is that bugs that hatch on the lake get washed over the spillway and feed the fish below the dam.
Trout are cold water species. When the water warms, they migrate into cold water spring seep pools, cooler water stream tributaries or out to a lake to get to their comfort zone. If they can’t migrate to colder water, they can die. Once again, sushi!
A second problem is that the natural migration of aquatic organisms is stopped by dams. Whether it’s the fish, invertebrates, minnows or other stream critters, dams can stop their natural migration up or down stream. This results in a loss of diversity in the upstream reaches. The continuity of the stream habitat must be maintained to keep a sound aquatic community.
On the flip side, dams may prevent the spread of invasive species into a river system, like lamprey eels.
Brook trout, brown trout, rainbows (steelhead) and smallmouth bass all spawn in the streams at various times. Some spawn in spring and some in fall. They may migrate back to the lake or stay in the stream. Steelheads are rainbow trout that migrate back and forth from stream to lake. Cattaraugus Creek in western NY is known for its steelhead runs and smallmouth fishery. Dams can stop this natural occurrence from ever happening. There is talk of removing the dam in Springville NY to allow access to another 20 or more mile of habitat for trout and other fish. We have dams in our area that also limit fish passage.
A third problem is that dams can allow ice to form and build up. In spring thaws, flooding can occur due to the ice jamming. Fast running water tends to be open, meaning it’s not frozen over, so ice jamming is less likely.
Rich Redman is a retired District Conservationist for the USDA Natural Resources Conservation Service and an avid outdoorsman. His column will appear regularly. He may be reached at firstname.lastname@example.org.