Even with the help of a sea-turtle-ID chart, I cannot make a positive identification. I am guessing green turtle, but I feel it might be a hawksbill. I have several good photos -- as the turtle let me swim close for a long time -- but none shows the beak. It is a very small turtle; I estimate the shell length at about 18 inches.
Photo taken November 23, 2009, about 20 feet of water, Molasses Reef (buoy M8, the Winch Hole), Key Largo, Florida, water temperature 79 degrees.