For those wondering if a person can drown in that shallow of a spot...
My husband served for a time as a life guard while he was in the military. He did save a woman who was drowning. He said that when he was trying to get her to the surface, she was fighting to go downward, pulling him down with her. People lose sense of direction sometimes while drowning, so just swimming up to the surface isn't as easy as you'd think in some cases. We also have to remember that the water was very cold, so muscles don't work as efficiently, and also he was fully clothed, further weighing him down and effecting his mobility. Add intoxication, which I firmly believe was present, and reaction time slows even more.
An autopsy will determine a good picture of what happened, as the above post explains, but it's not a stretch to think that he could very well have drowned in water that shallow.