They compared the extinction rate to that of species living in tropical rainforests. Seventeen freshwater fish species are extinct, and one in ten of America's native mussel species are extinct. Scientists believe habitat loss could contribute to the extinction of hundreds of freshwater species by the end of the 21st century. Dams built to support navigation, generate hydropower, and divert water for irrigation block fish migrations, disrupt the transport of sediment and nutrients, and eliminate natural variations in river flow that trigger fish reproduction and build wildlife habitat. Dams impact four of the top five rivers on this year's list and have driven certain species of salmon and fish like the pallid sturgeon to the brink of extinction.
Many dams are insurmountable obstacles to migrating fish.
Levees built to control flooding destroy riverside wetlands and eliminate important spawning and feeding areas for fish and other species. Flood control projects imperil Mississippi River birds like the endangered least tern, as well as Rio Grande species like the endangered silvery minnow. Our country is at a critical crossroads. We are entering a new era of restoration. Scientists agree that the cornerstone of the Clinton Administration's salmon recovery plan must include breaching of the four dams to remove obstacles to migration, improve river conditions, and let the river flow more naturally.