Southwest of Phnom Penh off the southwestern coast, the snorkeling off the scenic and remote Con Dao islands are known for its clownfish, cowfish, moray eels, turtles, sharks, sting rays and scorpionfish. Con Dao has over 20 dive sites with water depths up to 20m.
The snorkeling on the Con Dao Islands is reached by a short flight from Saigon or Ho Chi Minh City. There is also a ferry option available. To reach the snorkeling in Vietnam by air, you will most likely need to fly into Tan Son Nhat International Airport (SGN) located north of Ho Chi Minh City. Alternately, you may be able to get a flight into Noi Bai Airport in Hanoi. Once in Vietnam, there are several domestic airlines, such as Vietnam Airlines and Jetstar, that have routes to the remote cities closer to the dive destinations. These domestic flights can cut a day or more off travel times by bus or train. With that said, the railways in Vietnam do happen to serve the coastlines reasonably well and might be worth checking into for your itinerary. Keep in mind that the Tourist Visa for Vietnam must be issued before arrive.
Overall, Con Dao Islands is the 5th most popular snorkel dive spot of all 7 snorkeling dives in Vietnam.