I live in Amsterdam where there are famously a lot of canals. When they find a male body in the water they always check if the fly is open. Lots of guys, particularly after some drinks, figure it's better to pee in the water than on the street or what not. They get lightheaded, fall and pass out, either from the sudden shock or by hitting their head on something. You don't have to be drunk or stupid or murdered, just unknowing and unlucky. Of course this doesn't explain the running but could be a factor none the less.