The only good places to snorkel on Phuket are on Kata Yai and Kata Noi beaches; otherwise, head for Phi Phi or the Similan islands. Corals and barnacles are very sharp and can cut deeply, so treat cuts immediately with disinfectant before they fester.
Another menace are sea urchins and there are lots of them lurking in the corals. They look like dark maroon pin-cushions with iridescent orange and blue eyes. Step on one and you drive a poisonus spine into you foot, causing it to throb and ache for a long time. The traditional village reatment is to pound the embedded spine with stones to break it up. Someone then urinates into a coconut and the victim immerses his foot in it, the uric acid diluting the poison. If you find this remedy extreme, try the one doctors recommend: go to a hospital.