While many factors have affected the salmonid populations in California’s Central Valley, a driving factor is the presence of large dams. As dams have been constructed over the past century as much as 95% of the salmonid spawning habitat has been lost. The pioneer John Marsh wrote in 1844: “The magnificent valley through which flows the rivers San Joaquin and Sacramento is 500 miles long …. It is intersected laterally by many smaller rivers, abounding in salmon”
By 1929, though G. H. Clark wrote in a CA Fish & Game Bulletin, “The San Joaquin, as has been stated, has known its glory as a salmon stream, but that era is past, and the system has fallen to the development of irrigation and power projects. The salmon have dwindled and will go on to complete extinction unless more stringent measures of protection are soon put into effect.”
“The river cañons, where the old bars were located, were romantic places previous to being disturbed and torn up by the gold-digger. The water was as clear as crystal, and above each ripple or rapid place was a long, deep pool, with water blue as turquoise, swarming with fish. Salmon at that time ran up all the streams as far as they could get, until some perpendicular barrier which they could not leap prevented further progress…..during spawning times, the salmon would accumulate so thickly in a large pool just below, that they were taken in great numbers by merely attaching large iron hooks to a pole, running it down in the water, and suddenly jerking it up through the mass. And that place was not an exceptional one; it was so at all places where there was any obstruction to free running. ” (Angel 1882, p 402)
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This map illustrates the historical extent of steelhead habitat as modeled by the NOAA Fisheries Southwest Fisheries Science Center (Lindley et al. 2006). Researchers defined parameters for rearing habitat then, using a Geographic Information System model, isolated the stream reaches that met the criteria of suitable habitat.
The blue lines identify the stream reaches that historically had the proper habitat to support summer rearing for steelhead. As the 20th century progressed, numerous large dams were built, essentially forming a ring around the Central Valley that salmon and steelhead could not pass. Although the dams provided flood protection, hydropower, and allowed the Valley to become the nation’s prime agricultural region, the fish lost significant habitat as each dam went up.
This site tells the story of each of the major dams and their effect on California’s natural salmon and steelhead heritage. This site also lets you know what you can do to help recover these iconic species. http://noaa.maps.arcgis.com/apps/MapJournal/?appid=ceebefd9685143daa5bf30d5a7e0c7fa