Koh Si - Similan Islands
Koh Si, tucked away in the Similan Islands, often gets overlooked for its flashier neighbours, but we’ve always found it a solid option when you’re after something a bit calmer. It’s mostly shallow, topping out around 12 meters, with wide, flat plateaus on either side of the island. Think big coral patches stretching out, dotted with rocky outcrops. On a good day, when the visibility really picks up, you can get some impressive schools of snapper here, sometimes even a big grouper cruising by. If the wider scene isn't quite as active, we usually poke around the rocks for seahorses, nudibranchs, or a well-camouflaged scorpionfish. It’s a pretty laid-back spot, great for extended bottom times or those days when you just want to take it easy.
- Location
- Similan Islands, Thailand, Southeast Asia
- Coordinates
- 7.983300, 98.766700
Marine Protected Area: Hat Noppharat Thara-Mu ko Phi Phi
Best Time to Dive in Similan Islands
The warmest water temperatures in Similan Islands occur in May, averaging 30.8°C. The coolest conditions are in January at 28.6°C.
Monthly Water Temperatures
- January: 28.6°C
- February: 29.0°C
- March: 29.6°C
- April: 30.6°C
- May: 30.8°C
- June: 29.9°C
- July: 29.6°C
- August: 29.3°C
- September: 29.0°C
- October: 29.0°C
- November: 29.2°C
- December: 28.7°C
Nearby Dive Sites in Similan Islands
- 8 mile rock
- Andaman Scuba
- Anemone Reef (reef)
- Anita s reef - 5-20m (reef)
- Anita's Reef - 10-25m (reef)
- Anti gravity Divers
- Ao Kon Ka Re
- Ao Nui - 17m
- Ao Sane - 5-18m (reef)
- Ayara Bay - 17m (reef)
- Banana Bay - 5-20m (reef)
- Barracuda Rock - 20m (pinnacle)
- Batfish Bend - 10-28m (drift)
- Bay 1 / Ao Ter (reef)
- Beacon Beach
Nearest Dive Centres to Koh Si
- ABC Phuket Diving
- Activity and diving centre
- Adang Sea Divers - SSI
- All 4 Dive - PADI
- All4Diving® Phuket - ["PADI"]
- Amazing Phuket adventures - SSI
Marine Life in Similan Islands
Home to 183 recorded species including 127 reef fish, 38 hard corals, 9 seagrass & algae, 4 sharks & rays, 2 other, 1 octopus & squid.
Notable Species
- Whale Shark (Rhincodon typus) - Sharks & Rays
- Staghorn coral (Acropora kosurini) - Hard Corals
- sorrah shark (Carcharhinus sorrah) - Sharks & Rays
- Staghorn coral (Acropora indonesia) - Hard Corals
- seagrass (Halophila ovalis) - Seagrass & Algae
- Dusky Parrotfish (Scarus niger) - Reef Fish
- Bicolor Blenny (Ecsenius bicolor) - Reef Fish
- Moluccan cardinalfish (Ostorhinchus moluccensis) - Reef Fish
- Staghorn coral (Acropora secale) - Hard Corals
- Staghorn coral (Acropora valida) - Hard Corals
- Staghorn coral (Acropora hoeksemai) - Hard Corals
- cymodocea (Cymodocea rotundata) - Seagrass & Algae
- Herringbone butterflyfish (Chaetodon triangulum) - Reef Fish
- Dollfus's octopus (Amphioctopus aegina) - Octopus & Squid
- Clown Tang (Naso lituratus) - Reef Fish
- Staghorn coral (Acropora solitaryensis) - Hard Corals
- Species code: Ea (Enhalus acoroides) - Seagrass & Algae
- Blue-scaled wrasse (Cirrhilabrus cyanopleura) - Reef Fish
- Argus Grouper (Cephalopholis argus) - Reef Fish
- Staghorn coral (Acropora austera) - Hard Corals
Recommended Packing List for Koh Si
Based on average water temperature of 29.4°C, currents 7 cm/s.
- Shorty or Rashguard - warm 29°C water needs minimal exposure protection
- Mask - essential for every dive
- Fins
- BCD - buoyancy compensator
- Regulator - your most safety-critical piece of gear
- Dive Computer - tracks depth, time, and NDL
- Surface Marker Buoy (SMB) - essential for boat pickups
- Dive Torch - useful for crevices and colour at depth
- Underwater Camera - capture your diving memories