Doesn't that all very heavily depend on the exact nature of the system the dam is part of? We all know of the environmental problems of the Assuan dam in Egypt.

Doesn't that all very heavily depend on the exact nature of the system the dam is part of? We all know of the environmental problems of the Assuan dam in Egypt. But that does not mean that properly planned dam cannot be very beneficial. One shouldn't just build a dam where it is convenient but with careful analysis first. There are plenty of places where a dam just means less cities flooded occasionally but otherwise has little eco system impact.