Koh Similan Scuba Diving

Boulder City

Boulder city is a submerged site about 1 kilometre off the east coast of island no. 3 and about 400 metres south east of Sharkfin Reef. Due to its exposed location it is possible to see almost anything on this Similan dive, including whale sharks and manta rays. If the current is running it is always an exceptional dive.

As its name suggests, Boulder City is a large, submerged granite outcropping with jumbles of boulders lying scattered around a flat sandy bottom. The rock is so geometrically cracked in places that it resembles an enormous loaf of sliced bread.

There is very little coral growth here except for branching green cup corals on the rock surfaces and golden gorgonian fans in the cracks and gullies. However, the algae growth here is substantial, meaning a prolific amount of grazers, including both nudibranchs and fish. The masses of unicornfish, butterflyfish and angelfish picking at the algae almost resembles cows grazing on the summer pasture.

In the deeper sections, the landscape changes a little and red and white whip corals become dominant. Here you can see small schools of Oriental sweetlips, some large moray eels, blue-lined snapper, barracudas, triggerfishes and filefish. Leopard sharks are frequently seen in the outlying sandy areas as well as white-tip reef sharks. There are many cleaning stations here, and these provide a great opportunity to get close to slender unicornfish, a fish that is habitually very wary of divers. Some of the smaller species that you can see are jawfish (an endemic species to the Similan Islands), purple and red fire gobies.

This is one of the more advanced Similan dives as there is no area of the site shallower than 10 metres. This means that Boulder City requires a little more careful planning than most sites in the Similans. It's a good idea to end your dive at the shallowest boulder outcrop in the centre of the site so that you don't expose yourself unnecessarily to the strong currents that can sometimes run here. There's often schools of yellow-dash and neon fusiliers in this area, as well as black damsels.

Boulder City Reef Basics: Large granite boulders
Depth: 10 - 40m
Visibility: 20 - 40m
Currents: Can be strong
Surface conditions: Can be rough
Water temperature: 26 - 29°C
Experience level: Intermediate - advanced
Number of dive sites: 2
Diving season: November to April
Distance: ~90 km northwest of Phuket, 65 km west of Khao Lak
Access: Liveaboards and daytrips

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