The power stations at those dams didn't produce much power to begin with, them being very old designs. Note that most of the tens of thousands of dams in the US are just old relics serving no function, that are very expensive to remove. I agree that it's not an environmentally friendly way to generate power.
There are lots of small dams that serve no purpose now. The one in the following link (in Maryland) was near where I grew up. It was just a dangerous eyesore (the circulation below the dam was a deathtrap). After it was built in 1907, it generated power for just 17 years.
