Impoundments support the types of invertebrates that do not require flowing water for feeding or respiration purposes. Invertebrates found in impoundments also tend to be able to tolerate warm water temperatures and relatively low dissolved oxygen. Mussels are among the most endangered aquatic organisms in North America, partly due to the fact that the greatest mussel diversity is found in flowing water habitats, not impoundments. The types and abundance of fish found in impounded systems depends on the characteristics of water found in impoundments. Different types of fish prefer different temperatures of water, especially for spawning.
Many fish have narrow ranges of water temperature at which spawning occurs.
Because impoundments may have relatively warm temperatures, warm-water species tend to dominate impoundments. An impoundment with cold water, however, will support cold-water species. Dams are major obstacles to the movement of fish, either upstream or downstream. Although the free movement of fish can sustain a healthy fishery, a dam may also be a barrier to the movement of unwanted invasive species. For example, the Orienta Dam on the Iron River in northwest Wisconsin prevents the further movement of sea lampreys up the Iron River from Lake Superior.