A new study sums up what scientists now know about the environmental effects of removing dams from rivers.
It concludes that rivers and fish respond quickly after a dam is removed, and the results are mostly positive.
"Heraclitus has said you can't step in the same river twice,"said study co-author Gordon Grant. "Well, you don't get exactly the same river back after you take a dam off it that you had before, but you can come pretty close. In some cases, it can even be difficult to identify in just a few years where the dam was."