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8 For instance, the mussels in the Tennessee River declined from 100 to 44 species after dam construction. On the Neosho River in Kansas, there were significantly fewer species in the impounded area behind lowhead dams than in the river upstream. Those species that survived were silt- tolerant while sensitive species had disappeared. 7, 28, 36, 46, 52 The first impact will be on the mussels that may have been living in the bed of the stream that was impounded. As it fills, the streambed becomes the deepest part of the impoundment and silt accumulates. Sediment accumulation of as little as 1 inch can kill upwards of 90% of freshwater mussels. 8 Growth is reduced as these deeper waters are colder and there is no flow to bring food. Reproduction is impacted as the impoundment will be stocked with fishes that are not the natural hosts for most native mussels. While some might argue that a pool in a stream is similar to the quiet waters of an impoundment, they would be wrong. An impounded lake begins shallow and gets increasingly deeper as it approaches the dam. Pools in streams begin shallow, get deeper and then shallow up again. They are connected to riffles or rapids or glides and there is flowing water with a variety of substrates. A second impact of impoundments is the alteration of the stream habitat downstream. Impoundments are built to control the flow of a stream for various reasons including flood control, power, and irrigation. The stream below the dam may experience low flows or fluctuating flows. At the impoundment will act as a sediment trap, the released water will be hungry for sediment and will result in streambed degradation. Water released through the dam is often cold hypolimnetic water that lacks the food resources needed by mussels. Another impact is the fragmentation of the stream. It was noted above that freshwater mussels depend on fishes to carry their young back upstream to maintain their populations. Many of these fishes are migratory and the dam stops their migrations. As a consequence, some host fishes either cannot move upstream to repopulate the stream or they cannot even get to the mussels to be infected with their glochidea. 51 I have observed that the Fragile papershell is common in the Big and Little Blue Rivers below the Blue Springs and Fairbury dams. This species uses the Freshwater drum (Aplodinotus grunniens) as a host that is found in these rivers. However, the Fragile papershell is virtually absent above these dams. It would appear that these dams have served as a barrier to the distribution of the Fragile papershell in the Blue River system.

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