Bad things can happen in clear water also. My wife and I once decided to wade across a slow moving section of a Sierra Nevada river, no more than 75 yards across, maybe a foot deep. We made it about 70 yards, then she stepped on a slime covered rock and went down on her fanny. While helping her up, I did the same thing. Her brand new 35mm auto camera was in a pocket, got ruined. Lucky for us, no injuries, and it was the middle of summer, in the 90's at least. Trying to make the best of a bad situation, we stripped off and went skinny dippin' while the clothes dried on a rock...