The islands are at 8°39′09″N 97°38′27″E / 8.65250°N 97.64083°E / 8.65250; 97.64083
The park is an archipelago consisting of 11 islands, occupying an area of approximately 140 km2 with a land area of about 26 km2. For convenience, the Thai Department of National Parks (DNP) has assigned numbers to the islands. From north to south, they are:
The Similans lie 70 kilometres off the coast of Phang Nga Province. "Similan" is a Yawi word meaning "nine". Ko Bon and Tachai were added to the national park in 1998.
Ko Similan is the largest island. The sea in the area has an average depth of 60 feet. Underwater it is full of rock formations and coral reefs in several shapes and forms, resembling such things as deer, leaves, brains, and mushrooms.
Above the water are found many diverse species such as the Nicobar pigeon, mangrove monitor lizards, flying fox and more.
Ko Huyong has the longest and widest beach in the park. However, the park prohibits any tourists from landing on the island as the beach is a place where turtles come to lay their eggs.
Similan National Park is famous for its dive sites. It has typically two different kinds of diving. East side diving consists of gently sloping coral reefs with sandy patches with the occasional boulder in-between. The west side is known for its huge underwater granite boulders with numerous swim-throughs. Maybe the most famous east side dive site is East of Eden, off island number 7. Elephant Head Rock is arguably the most famous west side dive site with a maze of swim-throughs and the reputation for spin-cycle like currents running in every direction.
Elephant Head Rock was named by Horst Hinrichs from Germany in the mid-1970s, founder of one of the oldest dive shops in Phuket, Santana Diving.
Other popular dive sites include North Point, Deep Six, Boulder City and the awesome pinnacles off Ko Bon and Ko Tachai.
The most important of all dive sites in the Similans, in reality part of Surin National Park, is Richelieu Rock, famous for its variety and abundance of marine life. Whale shark sightings are not uncommon here. However, since 1999, its once most beautiful dive site, Fantasy Reef, has been closed from all diving activities after its condition had significantly deteriorated. Park chiefs officially blame diving for the deterioration, while dive operators in the area claim that fishing boats, with or without permission, enter the national park during low season, when no dive operators are allowed in the national park. The national park also claims that the dive site suffered significant damage from the tsunami in 2004, and continues to keep the reef closed. Since only national park staff are allowed to dive Fantasy Reef, it has been impossible to confirm that statement.
Islands 1, 2, and 3 are closed to the public due to a turtle hatching protection program and reef conservation efforts. Island number 3 belongs to a Thai princess. Fishing is banned in Similan and Surin National Parks. However, fishing boats are constantly seen in and around the park. When diving, one can often find nets stuck to reefs and illegal fishing traps. In recent years many illegal fishing traps have been found outside the most common dive sites. They have contained among others trevallies, batfish, barracuda, golden pilot jacks, and triggerfish. Fishing traps seem to be overly abundant around Ko Bon and Ko Tachai.
Access to the Similan Islands is easiest from Tab Lamu Port, just south of Khao Lak in Phang Nga Province. The park headquarters is in Tab Lamu, which is a small fishing village, just 13 km from Bang La On in Khao Lak. Boats depart daily from the middle of October to the middle of May. The trip takes about three hours each way on slower boats or 70 minutes via speedboat.
During the diving season liveaboard boats head to the Similan Islands. These dive boats depart and return from Tab Lamu, Ko Lanta, Phuket, and Ranong and stay for several days at Similan National Marine Park.
The park is closed in the rainy season, from 16 May-15 October, every year. The island of Ko Tachai will be closed to tourists indefinitely beginning 15 October 2016 to allow it to recover from effects of its heavy tourist burden.