Located 1 km off the east coast of Koh Payan, Similan Island number 3, and about 400m south east of Sharkfin Reef, Boulder City forms a chain of submerged boulder formations. Due to its southern location in the Similan Islands group it is often the last dive site visited on a liveaboard trip before the journey back to Phuket.
Boulder City gets its name from the large granite boulders that are stacked on top of even bigger granite boulders sat on the sandy bottom. They provide an amazing underwater landscape and great Similan diving.
Dives at Boulder City can be challenging as the site is exposed and currents can be strong but for this reason it attracts bigger fish such as whale sharks and manta rays. Other sights to look out for include Napoleon wrasse, turtles, and trevallies hunting swirling schools of glassfish.
Giant barracuda, dogtooth tuna and mackerel are also common as this dive site has many cleaning stations. These stations also provide a great opportunity to see the very timid slender unicornfish up close. Some of the smaller species that you can see are jawfish, which is an endemic species to the Similan Islands, and purple and red fire gobies.
The boulders drop down deeper than 35m so typically the dive starts deep and gets gradually shallower as you work your way in and around the rocks. The boulders are generally smooth with few corals although there are patches of soft coral and crinoid growth. Golden gorgonian fans and sea whips feed in the currents at the sides and in the cracks of the boulders. Sea urchins can be found wedged into the cracks, along with lionfish, scorpionfish and large moray eels.
There is an abundance of algae growth here which attracts plenty of grazers, including both nudibranchs and fish. There are masses of unicornfish, butterflyfish and angelfish happily feeding away. In the deeper sections, there are many red and white whip corals and here you are likely to spot small schools of Oriental sweetlips, blue-lined snapper, barracudas, grouper, triggerfishes, parrotfish and filefish. Leopard sharks and Kuhl's stingrays are frequently seen on the outlying sandy bottom of the deeper areas as well as white-tip reef sharks.
As this is one of the more advanced Similan dive sites, it's a good idea to end your dive in the middle of the site at the shallowest boulder outcrop. Here you can reduce your exposure to the strong currents that are sometimes running. However there are mooring lines on the site too that can help with your descent and ascent. Longfin batfish, black damsels and fusiliers are likely to accompany you on your safety stop.
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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