Food processing and kindred operations were indicted as the cause of death of over 6.5 million fish in one case in Iowa. Acid mine drainage in the Potomac River is responsible for some 20 miles of virtually lifeless mainstream on a perennial basis. Reservoir construction for hydroelectric power and flood control has inundated many miles of streams, causing species shifts in the short term and sediment-filled lakes in the long term. Accelerated sedimentation of estuaries and rivers has required extensive dredging to maintain waterborne commerce. The resultant dredge spoils have been deposited on wetlands, frequently causing losses of detritus essential to estuarine food chains.
Urbanization is perhaps the most permanent of all habitat modifications.
It has caused miles of channelization, extreme changes in hydrologic regimes, and extensive non-point source pollution, as well as the filling of large inland and coastal wetland areas. Along with sedimentation, overfishing is probably responsible for the endangered species status of the shortnosed sturgeon. Steam generation of electricity is estimated to have caused up to 179 million fish deaths annually through entrainment at one plant in Connecticut, and up to 20 million per day at another. Annual losses at a New Jersey plant have been estimated at 150 million eggs and 100 million larvae of 24 species. Supersaturation of water by gases has been caused by thermal additions from steam electric stations and by the plunging of water through high dam discharges.