Interesting, I never thought about stagnant low O2 water in the river. There is a backwater where I normally have a lot of action at. This weekend, I saw no action there at all. The water happened to be very cloudy in there compared to the rest of the river. I believe it gets cloudy from the carp/sucker schools stirring up the bottom. The water had been low for a while. I wonder if the water has been very stagnant in there for a while and the disolved O2 is low.