use city water to power hydroelectric turbines
most large cities have water mains that have high volumns of 60 psi or better water flowing most of the time, if the cities installed turbines for generating electricity in these mains, each could generate millions of megawatts of power to use, sell, or otherwise distribute.
there would be no problems with fish or warming water or low water flow as we currently have with dams, lakes, and spillways.