Koh Samui's private snorkeling charters navigate forty-two islands in the Ang Thong archipelago, a national marine park gazetted in 1980 and sheltering waters that drop to forty-metre visibility during the November-to-April window. The limestone karsts surfacing across the Gulf of Thailand are remnants of Permian-era reef systems, their submerged flanks now colonised by staghorn coral, table coral, and barrel sponges that anchor schools of fusiliers, parrotfish, and occasional blacktip reef sharks. Semi-private yachts and speedboat charters depart Samui's northern piers between eight and nine each morning, cutting west toward Koh Wao and Koh Mae Ko, where sheltered bays hold visibility above thirty metres even as afternoon winds begin to stir surface chop. The conservation fee of three hundred baht, introduced in 2019, funds mooring-buoy installation and patrol-boat fuel across the marine park's sixty-five square nautical miles. Private operators work under Department of National Parks permits that cap daily vessel counts at each mooring site, spreading snorkelers across Hin Lad, Koh Tai Plao, and the north face of Koh Samui itself, where granite boulders create swim-through channels populated by sergeant majors and moon wrasse. Longtail boats access shallower reef plates near Pig Island, a sand spit off Samui's southeastern tip where water depth holds at two to four metres and visibility remains stable through midday. Koh Tao, thirty nautical miles north, anchors longer itineraries that pair Nangyuan Island's tri-bay sandbar with Japanese Gardens and Mango Bay dive sites. The journey crosses open water in forty to sixty minutes aboard speedboats certified for eighteen passengers, though private charters typically load six to ten. Coral recovery zones established in 2021 now prohibit anchoring within fifty metres of active reef structures, and guides brief passengers on no-touch protocols before each water entry. The park's hours—eight to four daily—align with tide cycles that bring nutrient-rich currents through the archipelago's channels during morning ebb, concentrating pelagic activity near drop-offs and promontories where deeper water meets shallow reef.