Maintenance problems exist with dams or for that matter with any power generation mechanism.
None of these are show stopper problems.
-Birds fly everywhere; can't hide from them. It can be hard to diagnose some of the problems they create.
"Robotic" cleaning is really not as common as the headlines make it seem. A couple of big projects have used them to target settled dust that can be removed without water. For most projects, the robotic systems don't pencil out and people default to paying a small crew every couple of months to go out and wash them.