Whats that bug in my pool?

i have a saltwater pool and i live on a cliff overlooking the ocean, last night when i went for a swim there was a little black thing about an inch long, and its about half and inch wide, hes got like little flippers, no its not a frog :), its really cute but what is it, have never seen 1 b4, is it maybe something that came out the ocean, its not even bothered by the chlorine, it just goes about its business lol