Why would you think a troll couldn't enter the water?

git gut.

Trolled by a troll... Seems fitting. Just get some wood arrows and a bow and kill the thing. They are weak against piercing damage so use it. Throw spears at them if you have to.

It will not despawn AFAIK. Gotta either kill it, sneak up on it, or make a run for the grave.

If you master dodging, killing it is entirely possible, you just may want to get a flint spear before doing so.

Someone else posting that it camped over there body. No idea of time limit. You should be able to draw it off though. It will only chase so far and then it should go back to its original location. Sleeping won't help as that doesn't seem to advance the rest of the game, just changes day/night cycle.

Best to go 3 stamina based foods so you can run more often. But don't let stamina go all to zero. You can walk for a bit and be alright if you have a decent lead from running.