While it is obviously true that dams impede salmon swimming upstream in the way they might have been able prior to the dam being built, there is also anecdotal information from people who remember the salmon flows before the dam was built, that dams—particularly in areas with dry summers where rivers often virtually vanished into warm slow streams inhospitable to salmon runs, such as the American and Klamath—have improved the salmon run by providing a reliable flow of water at the right temperature throughout the year.
Of course, the salmon runs associated with the Central Valley prior to the arrival of the European settlers were huge and productive for the California Indians, but given the necessary accommodations to allow people to build and to live in cities, creating our urban civilization, the building of dams will often help the salmon, not hurt them.
Also, if global warming predictions are accurate, the need for more cold water stored behind dams which can be released for optimal conditions during salmon runs, will become even greater.
California Salmon Could Be Harmed By More Dams
Science Daily — Spring-run Chinook salmon and other fish in the rivers of California's Central Valley could be harmed by more water-storage dams, according to researchers at Duke University and the National Oceanic and Atmospheric Administration.
The findings of a recent paper may serve as a cautionary tale to policymakers, scientists and resource managers currently embroiled in a debate about the construction of new dams in the region.
Robert S. Schick, of the University Program in Ecology at Duke's Nicholas School of the Environment and Earth Sciences, used analytical techniques from network science to study the relative importance of individual populations of salmon within the valley and examined how the addition of large water-storage dams blocked access to habitat and fragmented these populations over time.
"We found that fragmented populations became increasingly vulnerable to disturbance and extinction," said Schick, who co-wrote the paper with Steven T. Lindley of NOAA's Southwest Fisheries Science Center in Santa Cruz, Calif.