The cleanest and most reliable source of electricity was the one harnessed by Nicholas Tesla, the hydroelectric power of Niagara falls. He used existing water drop of the waterfall to power a turbine with attached generator. Some people might tell you that this is very rare occasion dependent only on the terrain, and creating a water drop for efficient electricity generation is impossible without creating huge dams to flood some valley.
This might be true using the 50's technology, however now we have something called plastic. From which we can build high pressure pipes or hoses. Now, instead of sectioning off a piece of terrain and flooding it, you can put a big pipe, on the river bed. One end of the pipe will be in the middle of the city, connected to the turbines and generators. The rest of the pipe would be simply sunk on the river bed, upstream, for a few miles, so the appropriate water drop would be reached. Many more pipes or hoses can be sunk to get needed flow. This will work as scaled up science experiment of connecting two jars with water and placing one jar higher than the other. The added twist being, that the connecting pipe would be submerged in the third water bowl most of the time, which means it is peacefully on the river bottom, not disrupting anything.
With this, without drowning any terrain, nor displacing people and animals, you can create so much pressure in the pipe to power an instant water dam equivalent in the middle of existing cities that are build around the rivers.
A simple fire hose can operate at the pressures of 250 psi / 17.2 bars. This pressure is equal to the water in a pipe 577 feet / 176 meters high. There are fire hoses of about 20" of diameter, and you can put few of them in parallel. If laid on the riverbed you can create using only this technology an equivalent to the 80% of the Hoover Dam ( which has 726 ft / 221 m water height ).
You can also use existing oil pipeline technology that operates at 800-1400 psi / 55.2- bar that equates to 1900-3200 feet / 560-980 meters of the water column height. The tallest water dam is around 980 feet / 300 meters high. Now imagine power equivalent of such dam directly in the middle of a city, without any changes to the surroundings, power losses due to transit lines, nor any displacement of families which can sometimes amount to about 1,000,000 of people in case of the recent largest dams.
Generation HEAL Pages 151-153