Identify this animal?

I opened my pool this afternoon and I found this strange creature swimming in the murky water. It looked much like a worm but really fat, it looked almost like a leech but it had lots of tiny legs. It was dark green in color - the same exact color of the water. It had two antenna like things on its head but they were flimsy, thick, and wiggled around like arms. It also screeched or made like a hissing sound when I scooped it up out of the water. It was around three or four inches long.