The park covers 140 km2 in total. In 1998, the park was expanded to include the two remote islands Ko Bon and Ko Tachai, but since "Sembilan" is Malay for "nine" this doesn't seem to stick in people's minds and those are not visited as often as the original nine.
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:
- Island 11: Ko Tachai
- Island 10: Ko Bon, AKA Ko Talu
- Island 9: Ko Ba-ngu, AKA Ko Bayu
- Island 8: Ko Similan
- Island 7: Ko Hin Pousar
- Island 6: Ko Payu, AKA Ko Pa Yu
- Island 5: Ko Ha
- Island 4: Ko Miang, AKA Ko Meang. Park HQ is here.
- Island 3: Ko Payan, AKA Ko Pa Yan
- Island 2: Ko Payang, AKA Ko Pa Yang
- Island 1: Ko Huyong, AKA Ko Hu Yong
The islands were created by upwellings of hot magma during the Tertiary-Cretaceous period some 65 million years ago, then smoothed by glacial ice and the erosion by the sea. The coral reefs are about 5,000 years old and hence the oldest in Thailand. In 1982, the national park was established and now it is scheduled to become a UNESCO World Heritage Site.
The 2004 tsunami left the islands and the underwater landscape almost unharmed, since the waters are very deep around the islands.
The nine granite islands are postcard perfect images of paradise, covered in tropical jungle and equipped with beaches of chalk-white sand. As if this was not enough, the views under the water surface are even more impressive and many people believe this is the best dive site in Thailand. Skin-Diver Magazine has acclaimed the Similans to be one of the ten most beautiful places in the world.
Flora and fauna
There is an enormous diversity of fish species. Underwater visibility is the best you will find in Thailand. You will see plenty of colourful fish such as lionfish and clownfish (Nemo), and if you're lucky you may spot a bigger one like a manta or even a whale shark. The corals in the area have largely fallen victim to coral bleaching in 2010 and have not yet recovered, though the fish still make snorkelling and diving worthwhile.
On Ko Huyong, the Royal Thai Marines run a turtle breeding facility and access to the island is restricted.
High season in the Similans is from Dec-Apr, when the monsoon stays far away. The best period to visit is Mar, when the winds are calm and the water clear. The national park is closed from 16 May-15 Nov.
As of 15 October 2018, the number of visitors to the Similans will be capped at 3,850 per day. All visitors must buy a national park admission ticket and insurance before boarding a tourist boat. No single-use plastic is permitted in the national park.
The Similans are closed to visitors during the rainy season, 16 May-15 October every year. In addition, Ko Tachai has been closed to the public for an indefinite period since 15 May 2016 to allow the island to recover from the destruction caused by excessive numbers of visitors.
Virtually every dive shop on the North Andaman Coast offers diving and/or snorkelling day trips and liveaboards to the Similans. Dedicated cruises usually start at four days and four nights (4D/4D) in length. Many shorter trips are available, often with operators who have a large vessel stationed at the islands who do regular transfers using speedboats. Consult dive shop listings in Khao Lak, Ko Lanta, Phuket, Ranong, and even Bangkok agents for information.
Fees and permits
The national park admission fee for foreigners is 500 baht per day (children 300 baht). For Thai citizens the fee is 50 baht, children 20 baht. A diving fee is an additional 200 baht per day regardless of passport. Most boats do not include this in their quoted price. Fees are paid to the authorities via your dive operator before the trip.
Once on the islands there is the option of using the marine park boats for transit between the islands. This is not totally reliable, but is a less expensive alternative.
- Diving. Under new rules implemented 2018-10-15, the number of divers in the park will be limited to 525 per day. Similan Islands diving is famous and high on the list of top dive destinations. The Andaman Sea has perfect water conditions that make underwater visibility extremely high and suitable for diving and snorkeling. The seawater has an average temperature of 27 °C during the open season.
- Ko Similan: 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: 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.
- Dive sites: Similan National Park is famous for its dive sites. It has typically two different kinds of diving. Eastside 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 one of the most famous west side dive sites, 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 the 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.
- Mu Ko Similan National Park Souvenir Shop (Ko Similan). A small souvenir shop on Ko Similan sells small gift items.
- Mu Ko Similan National Park Restaurants (Ko Similan, Ko Miang). Daily when the park is open to visitors, 08:00-20:00. The facilities on the islands are pretty basic. You will find restaurants on Ko Similan and Ko Miang.
- No overnight stays. In 2018 all overnight accommodations in the islands were demolished and the number of visitors is now limited in order to preserve the environment. Admissions are capped at 3,325 one-day tour visitors and 525 scuba diving tourists.
See the Stay safe section of the scuba diving article for diving safety tips. The islands are closed from mid-May to mid-October each year. Tour operators going to the islands during the closed period are breaking the law.
The Surin Islands, which lie 40 km north of the Similan Islands. Restrictions on the number of visitors to the Surin Islands are anticipated.