 Large @-@ scale irrigated agriculture was introduced to the Central Valley in the late 19th century , and led to the construction of numerous state , federal and privately owned dams . Water demand has often been higher than the river 's environment can sustain . Salmon have been blocked from migrating and riverside habitat has declined dramatically . Recent years have seen habitat conservation work , mimicking of historic streamflow patterns , and the establishment of a salmon hatchery , in the hopes that the river 's health can be protected from further damage . 
