Adult salmon, which have been living in the Pacific Ocean, enter the mouth of the Columbia River and swim upstream to spawn. Fish ladders (left) help the salmon around hydroelectric dams by providing a series of stairstepped pools. The salmon spawn (above) either through natural propagation in streams or in hatcheries. To increase the supply of salmon eggs (below), hatcheries collect fish along the way and artificially spawn eggs. The young, called `fry,' are cared for in the hatchery. Once old enough, the young salmon (smolts) begin their trip back down the Columbia to the ocean. Dams (such as the McNary above) lengthen the time of the journey, exposing the smolts to predators and disease and destroying some of them as they pass through hydroelectric turbine blades. Deflector screens (right), such as these at Bonneville Dam, can divert most of the young migrants around the turbines. A target rate of 90 percent survival for fish at each dam is now being met. In 1971, the US Army Corps of Engineers began transporting the smolts around dams by truck (below) and barge. Despite these measures, it is estimated that only 23 out of every 100 fish survive to reach the ocean.