I'm in the Skyview Temple, in the first three connected rooms -- the middle room is the one that contains the map, the rooms to the left and right contain some skulltulas and pink switches.
Unfortunately I raised the water level (twice) before I realized there was another pink switch in a hole or tunnel at floor level in the room to the right...
I don't have the Water Scale (or whatever it's called) yet, so I don't seem to be able to dive. But there also doesn't seem to be any way to lower the water back down (hitting any of the switches again has no effect).
So it would seem I don't have any choice but to start the game over from scratch. Has anyone else encountered this?