Hong Island's emerald lagoon—Koh Hong Lagoon—sits at the centre of an 8.5-square-kilometre archipelago within Than Bok Khorani National Park, accessible only by boat and protected since 1991.
The lagoon's entrance is a narrow limestone channel four metres wide at low tide, opening into a circular basin 300 metres across, ringed by vertical karst walls that rise 120 metres. Thai fishermen named it "Hong," meaning room, for the enclosed water that once sheltered boats during monsoon season. The archipelago includes Pakbia Island, whose crescent bay holds a 400-metre beach of crushed coral and shell, and Lading Island, known for its shallow reef system extending 80 metres offshore at depths of two to four metres.
A hong island tour private allows departure times outside the standard 09:00-14:00 window when group boats converge. The conservation fee of 300 THB per person, collected at park checkpoints, funds reef monitoring and waste management across the island group. Private longtail charters typically seat four to six passengers and navigate shallow channels inaccessible to speedboats. Speedboat charters seat eight to twelve and cover the 12-kilometre route from Ao Nang in 25 minutes, compared to 45 minutes by longtail. Both vessel types moor outside the lagoon entrance; guests transfer to kayaks or swim the final 50 metres into the basin during mid to high tide.
The lagoon's clarity peaks between November and April, when Andaman Sea plankton levels drop and visibility reaches 12 metres. Afternoon light enters the basin between 13:00 and 15:00, illuminating the turquoise gradient produced by the 10-metre depth transition from the channel to the basin centre. Pakbia's beach remains shaded until 11:00 due to its western exposure, making it a preferred lunch stop. Lading Island's reef harbours sergeant majors, parrotfish, and occasional blacktip reef sharks in the one-to-two-metre shallows. The park prohibits anchoring within 30 metres of coral formations, and all boats must depart by 16:30 when the park closes.
6 hr
