Sure. Closed loop, fresh water going up and down. If there are dam concerns, the water can be pumped into the other reservoir.

Off river, closed loop pumped hydro does not impact existing fish, nutrient or water usage pathways, or people upstream or downstream.

Fresh water is not toxic, so having reservoirs of the stuff is just like having ponds with water levels that go up and down. They don't and can't turn into Superfund brownfield remediation sites.