The Ways Dams Harm Fish
On the most basic level, creating an impassable barrier on a waterway prevents migratory fish like salmon and steelhead from accessing their historic spawning habitat. Most dams were built before we understood the devastating effects they would have on river systems. And most were built before laws such as the Endangered Species Act existed. Today, large dams along the edge of the Central Valley block access to more than 70 percent of historic spawning and rearing habitat for salmon and steelhead.
A warming climate will result in a decrease in snowpack storage and a corresponding rise in winter runoff, which will increase the challenges of managing reservoirs for flood control, water supply, and summer hydropower. Rising temperatures will also make it harder to provide cold water for fish.
For too long hatcheries were placed below dams as "mitigation" for blocking upstream spawning and rearing habitat. Over time the science has made clear that, in most cases, hatcheries do more harm than good primarily due to diluting the gene pool of wild fish and reducing population resilience in the process.
RESTORATION