Many U.S. rivers have been deepened and widened for flood control or to accommodate barge traffic, creating artificial channels that don't support native species. Federal engineers have proposed turning Clear Creek in Texas into a channel. Riverbanks are often lined with tree branches or crushed rock, known as riprap, to prevent erosion. But it crowds out streamside trees whose leaves and fallen branches are crucial to the food chain. Stretches of the Missouri River are being lined with riprap.
Scientific studies lend some weight to the group's claims.
A spokesman for the hydropower industry said many of its electricity-generating members take steps to make dams friendlier to wildlife, such as adding extra oxygen to the water. David Tuft of the National Hydropower Association said dams also provide clean power and flood control.