South of Phuket Town and Ko Lon Island in the Andaman Sea, the snorkeling at Koh Hae is very popular. Also known as Coral Island, the island of Koh Hae is close to Phuket and tends to get very crowded with day-trippers from Phuket Town. The island is best enjoyed before the day-trippers arrive and after they depart for the day. So, it might be wise to plan to stay overnight at the Coral Island Resort. To access Koh Hae island from Phuket Town (15 min), hire a speedboat. Look around for booking packages that include both the boat transfer, resort and meals (even day trippers can get a package of boat transfer and meals).
While the main beach in front of the Coral Island Resort can be very crowded, the ends of the beach aren't too bad and the snorkeling is very good. If the crowds are too much for you to take, try doing the 15 minute hike to the east over to explore the Banana Beach snorkeling. This Banana Beach shouldn't be confused with the other one on Phuket Island located northwest of Phuket Town.
To reach the snorkeling in Phuket Island by air, fly into Phuket International Airport (HKT) which is located north of Phuket Town on the north end of Phuket Island. From the airport to your hotel, you'll most likely use a regular taxi car. There is also an Airport Bus to the Phuket City bus terminal #1 and does stop at the Pearl Village Hotel complex. The public bus called Song Taew also runs to the main beaches, and for instance, can be picked up from the local bus terminal in Phuket Town in front of the Central Market on Ranong Road. They run about every 30 minutes. For public transport between beaches, you'll need to use the Tuk-tuks (communal pickup trucks), which have the exclusive rights for inter-beach transport. The rates charged by Tuk-tuk drivers will seem quite high. While it may sound like a good idea to rent a car, it is generally considered to be quite dangerous to drive yourself around with all the steep winding poorly maintained roads.
Overall, Koh He is the 13th most popular snorkel dive spot of all 13 snorkeling dives in Thailand.