Reddit mentions of Power Politics (Second Edition)

Depends on what's there and what you value. It basically sacrifices the current hydrosphere of whatever waterway you're separating, and you get two lesser, out of whack ones. Any migrating aquatic species will die off or be a pitiful reminder of what once was. Ecosystem elements that depend on a dry season or flood season will be significantly messed up. And if you have a particularly dry year or three, then dams might not even serve their functions for power, navigation or water for crops.

Then there's the social element. It's pretty hard to find a place to do this that wouldn't displace people, usually the poor people who already have hard lives. B Street talks about this around the construction of Washington state's Grand Coulee Dam on Native American land. Arunhati Roy's book Power Politics focuses on India but documents this on global scale.

There's an efficiency factor, too (both economic and functional), where big dams work much better for generation, navigation and irrigation than small ones. They tend to involve corporations like Bechtel, Halliburton, KBR, etc who tend to be in the business of politics because they require government cooperation and budgets to do what they do.

I live in Seattle. We have cheap and clean power because of our dams. You can run a boat from the Pacific all the way up the Columbia to Idaho because of these dams. But the salmon runs have been decimated. Lots of people just had their land taken from them (and given hardly anything in return) for these projects. They're also insanely expensive to replace. As several of these things have silted over or reached structural failure, we've started to remove them. I think solar and wind power are better ways to go.