Wading...Swimming was not clarified in the scenario presented. In fact by the description of the buck's struggle it was easy to infer that it WAS swimming..either way....whatever

From the start a hunter is taught about the "fair chase". In this case I would not shoot at the deer so close to the water, so as not to loose it but also because the animal has exhausted himself from the escape of the ice/water. So I would definately wait, noting his location, until the next day. Then I would stalk him as best of my ability, if located then I would attempt to get within my range then take the shot. This way I would feel good in that I shot this great animal after giving him a good chance to recover and not having shot a trophy buck who was handicapped as he crossed the river. would you shoot a trophy caught in a trap? As a person who has hunted for the last 51 years and one who is instilling in his Grandson the ethics of a good sportsman I would not see myself worthy of such a trophy had I shot him as he left the water. A clean ethical kill is worth more than one where the deer was at a disadvantage. We as sportsmen owe this much to the sport we so much cherise and want to preserve.

I have seen a lot of comments on “fair chase”. I can’t help but feel that we might be taking that a little far.
In the wild, predators hunt the weak, tired and disadvantaged. This is the way it works. Shooting a tired buck is not even close to shooting a buck in a trap.
Besides, aren’t you hunting with a rifle? How is that “fair”. Are you using a scope? Tell me that isn’t an unfair advantage? I heard an anti-hunter once say, “if you wanted to make it fair you would go out with no clothes and no weapons and wrestle them to the ground.”
I personally feel that this is a ridiculous notion, but so is the idea that shooting a tired buck is “unfair”
If he is so exhausted that he can’t run away or collapses on the bank of the river, he won’t survive winter. So you could harvest him or let winter do it.
As a predator, I take every advantage I can get. (camo, scent killer, game calls, decoys, etc.) If you don’t want to shoot the buck then don’t. I only ask that you simply leave it as a matter of PREFERENCE (which it is) and not a matter of ETHICS (which it is not).

@ npaul:
I agree, it may be fair to shoot a tired buck. And if I based my personal shooting decisions on rack size, I probably would have a few mounts. I still hunt for meat, not horns. If the right shot presents itself, I will be eating fresh tenderloins after they have had a chance to age properly. I still think they taste better when they are calm and rested, not after they have been working hard to stay alive.

As I posted in the Ice scenario, I had a Buck come across a river. He lost his footing and almost went under. He did make it across, he RAN over to his scrape looking for the Doe that he could smell and sounded good enough to risk his life to swim for. I watched him cross, I watched him nearly slip down the river. Then I watched him drop when my arrow found his vitals. I waited for him to cross, I waited for a perfect shot. I waited for a perfect BUCK!