Working Knowledge; October 1997; Scientific American Magazine; by Rainey; 1 Page(s)

Asingle man-made barrier can exterminate all migratory fish trying to move up a river. Just one dam bigger than a few feet tall will block salmon, for example, from ancestral spawning grounds, eliminating all traces of the fish from upstream waters.

Historically a highly valued food source, salmon have been getting help. They have been raised to higher water levels in special fish locks, pumped into tank trucks and driven upstream and, most effectively, provided with fishways or ladders that surmount a dam in steps the fish can handle.