Koh Kood anchors the southeastern edge of Thailand's maritime frontier, where the Gulf of Thailand yields to Cambodian waters and the coral shelf drops steeply into the Sunda Trench.
The island's snorkeling grounds gained protected status in 1982 when the Royal Forest Department designated 68 square kilometers of surrounding seabed as Mu Ko Rang National Park, forbidding trawling and installing mooring buoys to prevent anchor damage. Hard coral coverage here reaches 60 percent in surveyed transects, double the regional average, sustained by nutrient upwellings and limited coastal development.
Most Koh Kood snorkeling tours depart from Bang Bao Pier on the island's northwest coast, targeting three primary zones within the marine park. Koh Rang Yai, the park's largest island, shelters staghorn thickets in 2-5 meter shallows where blacktip reef sharks patrol at dawn. Koh Rang Noi's eastern wall hosts table corals spanning three meters, their undersides dense with banded cleaner shrimp and porcelain crabs. Ao Phrao, a crescent bay on Koh Mak's southern flank, functions as a nursery site for parrotfish and juvenile snappers. Visibility averages 15 meters November through April, dropping to 8 meters during the monsoon months when plankton blooms dim the water but draw manta rays into the shallows.
Commercial snorkeling operations emerged on Koh Kood in the late 1990s, initially serving backpackers willing to overnight in beachside bungalows without electricity. Speedboat services from Trat's Laem Sok Pier, inaugurated in 2006, compressed the journey from five hours by cargo ferry to 90 minutes, opening the island to day-trippers. Today's fleet splits between longtail conversions running budget half-day circuits and fiberglass speedboats equipped with freshwater showers and cushioned seating, typically capping groups at 15 passengers to comply with park regulations. The 200-baht conservation fee, implemented in 2019, funds reef monitoring stations and funds seasonal closures when coral spawning aggregations form.
Operators schedule departures between 09:00 and 10:00 to exploit morning light, when oblique sun angles illuminate reef topography without surface glare. Most itineraries sequence three snorkel stops across four hours, interspersing swim time with fruit service and shallow-water instruction for novices. Thai-flagged vessels are required to carry VHF radios tuned to channel 16, oxygen kits, and one certified guide per eight snorkelers. Booking patterns concentrate heavily in December and January, when Northeast monsoon winds flatten the Gulf and European holidaymakers fill Koh Kood's 400-room accommodation inventory.
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