Most implementations of hydroelectric power involve cutting off and severely degrading the habitat of aquatic life, both upstream and downstream. Societies depend on these resources so it's hard to justify calling hydro power sustainable in a general sense. To those negatively impacted by the dam, it rightly feels like a ruthless power grab by outsiders coming to steal water and energy without any thought for the livelihoods that are destroyed.

Of course hydro power can be done correctly, assuming the collaboration of all the stakeholders in the watershed and careful tradeoffs. How many dams were built with such an equitable process?

Given hydro power's well-documented negative impacts, and our arsenal of other truly renewable energy sources, damming new rivers should be a last resort. In the US at least there is a strong trend of dam removal - many ill-considered hydro projects are costly to maintain, an economic loss to society as a whole, and a detriment to the environment. Quite far from any feasible definition of "renewable resource".

I thought California was running out of water because so much of the water rights are being utilized for agriculture.

Would it be possible for them to utilize hydro significantly without destroying their agricultural industry?

California is already using as much hydro power as is available for it to use. That use all happens upstream from the agricultural use; they do not compete. Agricultural use competes with wildlife and fishery, instead.

California also generates a really large amount of its power geothermally. We don't hear much about the many mature geothermal projects.

I thought Cali was killing off hydro by attrition because they say it damages river ecosystems?

Why ? is there a stated reason

Because of ecosystem and water footprint impacts associated with dams, in conjunction with the operational requirements of power generation. Dams obviously convert a river into a lake and impede/alter natural migratory patterns. Less obviously, hydroelectric power generation dictates a pattern of water release that is at odds with other demands on water usage, for human and natural usage purposes. (You can imagine that downstream environments might benefit from water flow which is more steady, or which follows natural rhythms; this is in conflict to some degree with grid demand for power.)

That's not zero carbon though if your carbon usage some other thing may have to traded off.

Utilities are required to buy a certain percentage from renewables. I think California wants to encourage more growth from solar and wind.

Still going to need base load - so CA is going for NNB (nuclear new build ) for that.