I have seen tape of a buck drowning a doe when he was trying to mate with her. But i think it would be hard for that buck to hold down the other buck underwater to drown it they are both big boys and its not that deep of a creek. Not saying it can' t happen but i don' t think that deer died of drowning (he might of died during the fight but from some other cause for example stress of the fight could of gave him heart failure) i am just saying its unlikey that is what happen.