The coast around the Andman & Nicobar Islands is home to some of the best coral ecosystems in the world. Many of the islands are surrounded by reef fringes, often separated from the shore by lagoons. The coastal area is also rich in marine flora and fauna, which are best seen while snorkelling and scuba diving off the islands. However, scuba diving is allowed only in areas permitted by the Andaman & Nicobar Administration.
One of the most easily accessible snorkelling and diving site in the Andaman & Nicobar Islands is the Mahatma Gandhi Marine National Park (MGMNP). Located in Wandoor, about 30km from Port Blair, it is thus a popular attraction on any Andaman and Nicobar trip. But do remember photography and diving are allowed only in the islands open for tourists Jolly Buoy and Redskin on payment of prescribed fee. According to most visitors, the marine life is so rich in this area that even on a snorkelling trip, one can see large shoals of colourful fish among the corals. The corals usually grow up to a depth of eight metres but some even go down to 40 metres. Some of the commonly seen marine fauna include jellyfish, starfish, sea anemones, sea cucumber and sea urchin. The park is also home to dolphins, turtles and sharks. If luck permits, you may also catch a glimpse of the endangered dugong (sea cow). Usually, November to May is the best time to go diving here.
Cinque Island, with up to 80 feet visibility into the emerald depths, is one of best deep diving destinations in the Andaman & Nicobar Islands. Amateurs can go diving off the South-east Reef here where hard and soft corals abound, and are dense on the rocks up to a depth of 16 metres. North Island is also a popular point.
No Andaman and Nicobar trip is complete without a visit to the Havelock Island, about 2.5 to 3 hours ferry ride away from Port Blair. Some of the best snorkelling and diving sites are located off Havelock Island. Mac Point is known for its hard corals. The fringe reef Aquarium gets its name from the heavy fish traffic found in the area. Barracuda City with its hard and soft corals, fish and turtles is one of the best places for inexperienced or amateur divers. The huge rock at Seduction Point teems with aquatic life. Here you will see staghorn corals and their associated marine life, including the Napoleons. Lighthouse is a popular night dive zone. A huge submerged rock, aptly named The Wall, drops down to 55 metres at maximum depth, shelters dense forest of soft corals and plenty of fish. A mass of hard corals, the Pilot Reef, has canyons stretching out at about a depth of 24 metres. You may see sharks at the Pilot Reef or at the Minerva Ledge, which is also a huge block of hard corals.
Other areas where one may go snorkelling and diving are Snake Island near Corbyns Cove beach in Port Blair, Bala Reef on the western side of the Little Andaman Island, Rutland Island (it also has a shipwreck), Corruption Rock and Fish Rock.
Andaman & Nicobar Island administration always advises that snorkelling and diving activities must be carried out in the presence of trained and certified experts. According to an advisory issued by the government tourism department, tourists opting for snorkelling must be accompanied by a trained snorkel guide licensed/certified by the National Institute of Water Sports.
The website of Andaman & Nicobar government maintains a list (https://www.andamans.gov.in/ScubaOperator.html) of registered scuba divers.