[czinck]

As zwieback said, a lot of the dams just aren't that useful, for a bunch of reasons but biggest is that they're just too small. On top of that, at least for the Washington dams I'm more familiar with, the power generation doesn't match up with need. Most of the river flow is over the winter and spring (that's when it rains/snows and then more rain and melting snow) and in the late summer when electricity use is highest the dams don't have enough water flow to be really productive. Worse yet, some of the oldest dams are even more limited because there's too much mud in their reservoirs.

Nothing insurmountable (dredge the silt, build them bigger so the reservoir lasts until the fall, etc), but it just means the most cost effective way to help the salmon is tear down a lot of these dams.