are there any rivers left to build hydroelectric dams in the u.s?

There are 80,000 dams across the U.S., and only 3 percent have the turbines and other equipment necessary to produce power from the water that flows through them. Powering these facilities is a way to increase our nation’s supply of renewable energy by maximizing our existing infrastructure and without the need to build new dams.

Yes there are rivers that might be suitable that don't have dams because people are fed up with dams ruining the ecology of the area and wrecking the few wild rivers left.

But your idea of putting another dam further down falls apart because most rivers with dams have them only at the best location for a dam and there is not another place where the shoreline/bedrock/shape of the land can support a dam and the reservoir behind it.

The suggestion in the other answer that power generation be put in the 80,000 existing dams falls apart because most of them are just water control dams without much head - needed for power - and certainly missing the structure to feed the pressurized water through the dam to the generators.

It appears the subject is very controversial. Likely the truth is in between. From the promoters of more hydro electric dams, one project, will produce 72 megawatt at a cost of $400 million dollars. That is $5.56 per watt, about the cost of a small one watt solar panel which produces about 8 hours per day. Comparing other costs and impacts may be about equal in a few locations. Will this dam produce 8 hours per day average? They didn't say, but that is a reasonable guess, making it about equal with solar PV = photo voltaic.

Wind turbines are about twice a good as hydro or solar in West Texas, but our Federal government appointed a committee to decide if we should build a power line from West Texas to a populated area. Other locations in the world's best wind corridor were getting serious proposals, before the recent world wide recession began.

Yes, there are some locations where we can get hydro power, with some subsidies from the USA government and some sacrifices by the local population, but that is how it is with all sources of electricity, with the possible exception of DIRTY coal. My guess is we can get one more percent of our electricity needs from hydro, before the costs and bad side effects become unreasonable. Neil