It’s all water over the dam – but how, when it falls has huge impact on salmon
By adjusting water discharges in ways designed to boost salmon productivity, officials at a dam in central Washington were able to more than triple the numbers of juvenile salmon downstream of the dam over a 30-year period. The investigators say the results also show how the existence of dams can actually improve salmon survival. Prior to the development of the hydroelectric system, water flow in the Columbia could drop very low in winter. These low flows, when combined with temperatures below freezing, likely resulted in mortality of eggs and young salmon still in the gravel. Current dam operations maintain minimum water flows that are more than twice as high as historic levels during winter, which keeps young fish in water more consistently than what might occur naturally.