Hydroelectric is a storage device, not a power source.
The source is solar energy.
What environmentalists have a problem with is cheap energy for their human livestock so that can live free and independent of them.
Is that true? I thought the released water flows through a turbine and spins it and generates electricity?
Sounds like I have misunderstood hydroelectric? Can you point me towards resources to better understand that?
Actually, other than geothermal and nuclear, pretty much every energy source works its way back to solar (and that includes wind).