Substantial amounts of water are necessary to address obligations to Indian nations and tribes. Others, however, are banking on local grassroots efforts for solving the West's water problems, watershed by watershed. One reason for the pessimism is the magnitude of the problem. More than 20 of these western fish have become extinct over the last century and another 100 are considered imperiled. Loss of these fish would mean destruction of 70 percent of all fish species native to watersheds west of the Rockies.
Some people blame ocean conditions, sea lions and birds for the disappearance of native fish.
But most of these imperiled species never see salt water. The declines followed the destruction of their habitats on land, starting over a century ago. Minckley writes that starting in the 1800s, timbering, plowing of prairies and livestock grazing altered natural vegetation at the watershed scale. Flash floods became common due to rapid runoff. Development concentrated along rivers near travel routes and towns where diversions, dams and other structures altered patterns and volumes of discharge, and began to act as barriers to fish dispersal.