Ninety-nine percent of Con Dao's marine territory sits inside a national park boundary established in 1993, enclosing sixteen granite and volcanic islands and twenty-four thousand hectares of reef and open water. The archipelago lies one hundred ninety kilometers off the southern coast of Vietnam, far enough from industrial runoff that visibility on calm mornings reaches thirty meters. Green sea turtles — Chelonia mydas — nest on Bay Canh Island between May and October, and juvenile hawksbills forage year-round in the shallow staghorn beds off Hon Cau and Hon Tre Lon. The Con Dao snorkeling trip itineraries fan out from the main harbor at Vo Thi Sau pier, where the national park headquarters maintains a dive and snorkeling permit checkpoint. Most operators depart between seven and eight in the morning, timing arrivals at outer islands to coincide with slack tide and the northeasterly shadow that holds until midday. The water temperature hovers between twenty-six and twenty-nine degrees Celsius, warm enough to snorkel without a wetsuit but cool enough that thermoclines form over drop-offs. The reefs descend in tiers: elkhorn and table coral in the shallowest three meters, boulder and brain formations below five, and soft gorgonians clinging to vertical walls that plunge past twenty. Con Dao's isolation preserved its marine ecosystem through decades when coastal reefs elsewhere suffered overfishing and anchor damage. The park enforces strict no-take zones around Bay Canh, Hon Tai, and the western flank of Hon Cau, and boat operators follow designated mooring routes to avoid dragging chain across live substrate. Dugongs — Vietnam's rarest marine mammal — were documented in seagrass meadows near Hon Tai as recently as twenty twenty-one, though sightings remain infrequent. The more reliable encounters involve parrotfish, fusiliers, and the occasional blacktip reef shark cruising the channel between Hon Tre Lon and Hon Trung. Snorkeling access in Con Dao differs from Thailand's Similan Islands or the Philippines' Tubbataha Reef in one key respect: the Vietnamese government limits daily visitor numbers to each protected zone, and permits are allocated to licensed operators on a first-come basis. That cap keeps the reefs quiet but makes advance booking essential during the dry season, particularly between February and April when the South China Sea flattens and visibility peaks. The national park entrance fee — sixty thousand dong per person — covers both terrestrial trails and marine zones, a combined ticket model introduced in two thousand seventeen to fund ranger patrols and mooring-buoy maintenance across the archipelago.