There is a wide scope for snorkel and flipper fun on Koh Phangan as there is on the west coast an abundance of coral reef formation. Although not quite up to the standard of the great barrier reef there are a few colors to be found and certain areas have remained over time better than others. One of the most popular spots of Koh Phangan is the waters around Koh Ma which is a small Island on the West coast joined by a small sand bar to Maehaad Beach. Other good places are Haad Salad and Haad Khom where colorful coral reefs can also be found, ask along the beach for a place to rent the mask and flippers.
It should be noted that the reefs are often described as "soft coral" but are in fact very hard and sharp to touch. Not only should coral not be walked over for environmental reasons as it causes damage it could also cause injury to the snorkeler. Wearing a t-shirt when snorkeling is not only good for the sun protection but also offers a first safety stop against any coral you may be swimming over.
The array of fish can seem endless when exploring the underwater world, the huge amounts of small fish lead way to large reef fish and sometimes its possible to see large fish such as marlin, barracuda, trevelly, grunt fish and snapper. They are of little threat to the snorkeler and most often will be more surprised to see you then you are them.
At Haad Salad, Maehaad, Koh Ma and Haad Khom the areas for snorkeling are relatively sheltered and the water is normally calm and the currents few, care should be taken though and the current should be checked when entering the water. Koh Phangan can experience strong currents around headlands even in calm conditions and snorkeling should be restricted to inside of bays.