Scuba in Similan Islands, Thailand

The Similan Islands are a chain of nine granite islands located approximately 65 kilometers off the coast of Phang Nga Province in southern Thailand. The archipelago sits within the Andaman Sea and is designated as a National Marine Park, which restricts development and helps preserve the underwater ecosystem. The islands are characterized by steep granite formations that extend below the waterline, creating dramatic underwater topography with boulder formations, swim-throughs, and wall dives that range from 15 to 40 meters in depth.

The Similan Islands attract divers across all experience levels because the dive sites offer variable conditions and depths. The western side of the islands faces the Andaman Sea and typically has stronger currents and larger swells, while the eastern side provides more sheltered conditions suitable for building confidence. Visibility in the region averages 20-30 meters during optimal conditions, though it can range from 15-40 meters depending on seasonal factors and specific site conditions. The marine life includes reef sharks, groupers, snappers, rays, sea turtles, and various species of nudibranch and macro fauna among the coral and rock formations.

When you arrive, expect a boat-based operation rather than shore diving. Most divers access the Similan Islands through organized liveaboard trips or day-boat operations departing from Phuket or Khao Lak. The journey takes 1.5 to 2 hours by speedboat. The islands themselves have limited infrastructure—no hotels or restaurants operate on the islands due to national park regulations. The landscape above water consists of dense jungle vegetation and white-sand beaches, creating a remote atmosphere despite the popularity of diving operations in the area.

Local knowledge includes understanding the monsoon patterns that significantly affect conditions. The northeast monsoon runs from November to April, bringing the calmest seas and best visibility. During this window, the islands see peak diving activity and the most favorable conditions. Water temperatures during peak months average 79-81°F, requiring either a 3mm or 5mm wetsuit depending on personal cold tolerance. Wind speeds average 12-13 mph during February and March, creating moderate but manageable sea conditions. Currents are present at most sites and range from light to strong depending on location and tidal cycles, making current awareness essential for all divers.

The overall experience centers on technical rock formations rather than pristine coral gardens. Divers spend time navigating granite boulders, exploring crevices, and spotting smaller marine life within complex topography. The sites lack the soft coral abundance of other Thai destinations, but the geology creates memorable diving with unique visual characteristics. Most operators run two to three dives per day during liveaboard trips, allowing divers to experience multiple sites and return to familiar locations at different times to observe behavioral changes in marine life.