Salmon, I think throwing a disc in chest high lake water is pretty challenging.
Billolick, I'm not saying the rules should make you play from the water, I just want to have the option when they put a lake in between me and the basket to play from said lake. They give you that option in ball golf.
Presumably, the hole is designed specifically for that water to be O.B. Just as a hole might incorporate a paved area, a roped area, or anything else as mandatory O.B. If the designer did it right, the O.B. makes it a better hole, and negating it would make it a weaker hole.
We have a hole that is a 250' water carry, with the basket on an "island" between the water and the road (also O.B.). It's a bit of a thrill, because you must clear the water. It would play much weaker if a player came up 10' short, but could wade out into the water and putt from there.