Pigeon Island National Park, a twin-islet sanctuary 1 kilometer off Nilaveli's coast, shelters the largest surviving coral reef in Sri Lanka's northeast — 300 species of reef fish navigate staghorn and brain coral formations that withstood decades of civil conflict and monsoon erosion. The park earned its name from the rock pigeons nesting in coastal crevices, but beneath the surface lies the real draw: blacktip reef sharks patrol the shallows, hawksbill turtles glide through eel grass beds, and schools of fusiliers swirl around submerged boulders that rise 8 meters from the seabed. Conservation efforts since 2003 have reversed blast-fishing damage, and visibility now reaches 20 meters on calm mornings between May and September. Mirissa, 150 kilometers south on the island's underbelly, trades Pigeon Island's hard corals for a different spectacle — green sea turtles grazing on algae-covered rocks within 50 meters of Mirissa Beach. The southern coast's reef structure differs: patch reefs scattered across sandy bottoms, fewer vertical walls, warmer water year-round. Snorkeling in Sri Lanka tour operators here emphasize turtle encounters over coral diversity, and the approach works — sightings occur on 80% of morning excursions. The turtles, accustomed to snorkelers since tourism resumed in 2010, surface every 4 to 7 minutes, their carapaces encrusted with barnacles and remora fish. Trincomalee's protected bays — Uppuveli, Nilaveli, Dutch Bay — form a natural amphitheater where the Bay of Bengal's currents lose momentum, depositing sediment offshore and leaving the inner waters crystalline. The east coast's dry-zone climate guarantees flat seas from April through October, a 6-month window when even novice snorkelers can wade into chest-deep water and spot parrotfish, butterflyfish, and the occasional octopus within minutes. Pigeon Island remains the region's anchor site, but smaller reefs fringe the coastline — unnamed coral heads that local operators visit when park visitor quotas fill. The island's snorkeling infrastructure matured after 2009, when the war's end unlocked the northeast. Trincomalee and Mirissa now support year-round operations, each site calibrated to different skill levels and marine priorities. The Pigeon Island conservation fee, fixed at 25 USD for foreign adults, funds reef monitoring and turtle nest protection. Equipment quality has standardized — silicone masks, dry snorkels, flotation vests — and most operators provide underwater cameras to document the sightings visitors describe but cannot always name.