On the central eastern coast, the snorkeling off Nha Trang beach in the marine park is known for its soft and hard corals with plenty of small reef fish. Nha Trang is considered the home of diving in Vietnam.
There are numerous islands off shore to explore as well, such as the Hon Mun Island Marine Park. Within the Hon Mun Island Marine Park, there are numerous popular dive sites with waters ranging from 10m to 50m deep including Goat Roac, Moray Beach, Madonna Rock and Marine Reef. 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, Nha Trang is the 1st most popular snorkel dive spot of all 7 snorkeling dives in Vietnam.