there's 3 areas i know about. one is in the housing area at approximately 7:00 in the circle <see ranik's maps>. That area is the lowest skill, trains from about 50ish to 80ish or so.
the 2nd area is the beach on the shore. Those waters are shark infested if you go out. <see raniks' maps>The further out you go, the better the training. And the more risk you'll encounter Jaws. I'd say that area trains to about 100-400ish.
The 3rd is the area that leads to Peri'els shrine at approx 1:00 in the circle <see ranik's maps again> I'm not sure whats the upper limit. I do know that you can drown there, and you can't get all the way to the shrine with 300ish swimming.<survival prime but not a ranger>
"we're doing it for the good of mankind," said the philosophers of murder, waiting for the rest of the world to congratulate them"-Elie Wiesel <the gates of the forest>