Phu Quoc's southern archipelago holds fifteen islands scattered across the Gulf of Thailand, their granite shoulders rising from water that ranges between six and twenty metres deep. The An Thoi cluster—May Rut, Gam Ghi, Mong Tay, and Thom—became a gazetted marine conservation zone in 2019, protecting forty-seven documented coral species and more than two hundred reef fish. Visibility averages twelve to eighteen metres during the dry season, peaking between November and April when the northeast monsoon subsides and sediment settles. The reefs here are staghorn and table corals, brain corals, and soft gorgonians anchored to volcanic rock. Speedboat operators depart An Thoi Port each morning at half-hour intervals, cutting transit time to under twenty minutes per island. Tours follow licensed routes approved by the Kien Giang Department of Natural Resources, with mandatory briefings on buoyancy control and no-touch protocols. The best snorkeling tour Phu Quoc itineraries concentrate on shallow reef flats between two and eight metres, accessible to first-time snorkelers while offering enough topography—swim-throughs, coral bommies, drop-offs—to hold the attention of experienced divers. Operators supply silicone masks, dry snorkels, and short fins; most prohibit gloves to discourage reef contact. Four-island safaris spend ninety minutes at each site, alternating between sheltered lagoons and open-water channels where pelagic species—barracuda, trevally, occasionally blacktip reef sharks—patrol the outer edges. Two-reef itineraries focus depth over breadth, anchoring for extended sessions at Gam Ghi and May Rut, where hard coral cover exceeds sixty percent. The southern islands snorkeling routes avoid the cable-car corridor and hotel beaches, reaching sites that receive fewer than thirty visitors per day. Water temperature holds steady between twenty-seven and twenty-nine degrees Celsius year-round; three-millimetre shorty wetsuits are recommended for sun protection rather than thermal insulation. Phu Quoc coral reef tours operate under a tiered permitting system introduced in 2021, capping daily visitor numbers at each site and requiring operators to rotate anchorage points. The system has measurably reduced anchor damage and fish feeding, though enforcement remains inconsistent at the northernmost islands. The best operators—those running small-group charters rather than high-capacity ferries—adhere to the six-guest-per-guide ratio and conduct pre-departure buoyancy checks. An Thoi Port maintains a decompression chamber and a marine rescue coordination centre, though neither has been required for a snorkeling incident since 2023.