Many do consider Hydro Green... those folks tend not to be salmon fisherman... impoundments do create CO2, more than you might think. The adverse impacts of dams are massive, however.
It is a massive fallacy that water storage is the best solution. We have over 1,400 dams in CA. The most efficient dam sites have been built already. Moreover, most of those dams actually provide water for ag, not for drinking. Of the water that SoCal gets, only 12% comes from the Delta. Southern CA has absorbed an amazing amount of growth in the past couple decades without using more water. They use as much now as they did 20 years ago... they have conserved. We could do more of that in the North... we could also encourage central valley ag to use less, to plant less water intensive crops. Since almost 80% of CA water goes to agriculture, that is the place where the biggest potential gains come from.
The best place to store water is actually in the ground. Ground water storage is much less expensive than surface storage and much more productive.
Simple conservation measures do and would have a much more profound impact on increasing water yields.
B-
PS - here is an article about dams and CA water.
http://www...gename=FORDamLiesArticle