In most cases, riverine kinds of mussels cannot survive in lakes. So all the mussel beds in the upstream reservoir area of the dam are eliminated. Depending on the type of dam, releases from the dam may not mimic natural conditions, instead unnaturally high releases of water alternate with unnaturally low releases of water. Back to the top. Sedimentation and Pollution Agricultural production causes eroding soil to run off into rivers and lakes.
Bridges are also sites of high erosion and sedimentation.
Large amounts of sediment entering streams and rivers can bury gravel and rocky bottoms and smother mussels. Many kinds of mussels cannot live on muddy or unconsolidated sandy bottoms, they need the river bottoms to be rock, gravel, or firm sands. The sediment in runoff often carries pesticides with it, which further pollutes the water. Other contaminants such as PCBs, mercury and lead are deposited in waterways from industrial plant discharges. A wide variety of other toxic substances are released from industrial sites.