Eh, as long as you designed it with a reasonable factor of safety (say, highest temperature ever recorded at that location +5C, maybe) it’d be fine. I think the cost is a far, far bigger issue because the radiator necessary would be absolutely gigantic. Plus if you’ve got fans cooling it (so you can make it smaller) instead of passively cooling it, that’s another point of failure, although I suppose if getting river water relies on pumps then it isn’t any worse.