Koh Larn sits seven kilometres offshore from Pattaya, its western and southern coasts sheltering shallow coral gardens that survived the Gulf of Thailand's 1998 bleaching event and now host more than forty hard coral species. The island's position at the edge of the continental shelf creates a dual dive environment: beginner-friendly reefs at five to twelve metres on the sheltered western bays, and deeper drop-offs past fifteen metres on the exposed southern tip where visibility often exceeds twenty metres during the November-to-April dry season. Diving infrastructure arrived on Koh Larn in the early 1990s when Bangkok-based operators began running weekend trips to relieve pressure on the Phi Phi and Similan archipelagos. By 2010 the island supported five PADI-certified dive centres, most clustered around Tawaen Beach and Samae Beach where shore access and mooring buoys allow rapid deployment of beginner groups. The reefs here are shallow enough that a single-tank dive regularly exceeds forty minutes of bottom time, and the sandy substrate between coral patches creates natural navigation corridors that reduce the risk of disorientation. Hawksbill turtles nest on the island's quieter northern beaches between May and August, and juveniles are frequently sighted on the western reefs during morning dives. The Pattaya diving tour circuit now includes three-island catamaran routes that combine snorkelling at Koh Larn's Monkey Beach with deeper dives at Koh Sak and Koh Krok, two smaller islets five kilometres southeast. These full-day itineraries typically depart Pattaya's Ocean Marina between 07:00 and 08:00, reaching Koh Larn's western moorings by 09:00 to avoid the passenger ferry surge that peaks between 10:30 and 11:30. Beginner scuba diving packages centre on two-tank dives with surface intervals spent aboard the catamaran or on the beach, while advanced divers are steered toward the sixteen-metre wall at Koh Sak's southern point where moray eels and juvenile barracuda occupy the crevices. Water temperature in the gulf holds between twenty-eight and thirty degrees Celsius year-round, eliminating the need for thick wetsuits and making Koh Larn one of Southeast Asia's more accessible entry points for first-time divers. The island's reefs are not pristine—anchor damage and runoff from Pattaya Bay have degraded coral cover on the northern and eastern flanks—but the western sites remain robust enough to support resident populations of clownfish, parrotfish, and blue-spotted stingrays. Most operators now enforce no-touch policies and use permanent moorings rather than anchors, a shift that began in 2015 when Thailand's Department of Marine and Coastal Resources designated the waters around Koh Larn as a marine conservation zone. The regulations prohibit spearfishing and limit daily dive group sizes to twelve participants per instructor, a cap that has stabilised reef health without choking off access. Visibility fluctuates with the monsoon cycle: fifteen to twenty-five metres from November through March, dropping to eight to twelve metres during the southwest monsoon between June and September when plankton blooms cloud the water column.