RE: Safe to eat??
Drinking from a river doesn't contaminate an animal in nearly the same way that feeding from it's denizens would, and mercury warnings are based on extremely small amounts of contaminant anyway, the meat should be perfectly safe. We have mercury warnings on many bodies of water here due to the number of coal fired generating stations in the state. So far I've only heard of them being applied to fish, especially predatory species such as bass which consume other water dwellers and therefore have higher concentrations of mercury in their tissues. If drinking the water was sufficient then every beef steak and burger you've consumed would carry the same warnings since livestock drink from rivers too. I wouldn't lose too much sleep over it, deer are just as likely to drink from the nearest puddle as they are from a river.