Coral reefs There are 75,590
rai of coral reef in the gulf, of which five percent are considered to be in fertile condition. In 2010 severe coral bleaching occurred at most reef sites in the country. Bleaching of reefs in the Andaman Sea was more severe and extensive than that in the Gulf of Thailand. Scientists have determined that bleaching starts when seawater temperature rises beyond 30 °C for more than three weeks. Given the prolonged period of temperatures up to 32 °C at Ko Thalu in Prachuap Khiri Khan, five to ten percent of corals in the area are already bleached.
Water quality Coastal water monitoring results in 2015 from 202 sampling locations, collected twice annually, indicate that no Thai coastal waters were found to be in excellent condition. Sixteen percent of coastal water was of good quality, 72 percent was of fair quality, 9 percent was of poor quality and 3 percent was of very poor quality. The quality of all coastal waters exhibited similar percentages — most were of fair quality — except for the Inner Gulf of Thailand, where the coastal water was poor to very poor. In comparison to coastal water quality as measured in 2014, water quality has deteriorated. Some gulf waters off
Chachoengsao Province,
Samut Sakhon Province,
Samut Prakan Province, Bangkok,
Rayong Province,
Chonburi Province,
Phetchaburi Province,
Prachuap Khiri Khan Province, and
Surat Thani Province were judged to have coastal waters in "poor" or "very poor" condition.
Coastal erosion Thailand has 1,660 kilometres of coastline bordering the gulf. "Severe erosion", more than five metres of coastline loss per year, afflicts 670 kilometres of that total. At least some of the erosion is attributable to the clearing of mangrove forests to make way for shrimp farms.
Plastic pollution In February 2017, a 10 kilometer-long patch of plastic refuse was found floating off
Chumphon Province. Thailand is among the world's worst plastic polluters. More than half of "land-based
plastic waste leakage" into the sea originates from just five countries: China, Indonesia, the Philippines, Thailand, and Vietnam. The Thai Marine and Coastal Resources Department has noted that at least 300 sea animals on average—60 per cent of which are whales and dolphins—die from eating plastic fishing gear and trash each year. Thailand's Pollution Control Department (PCD) estimates that plastic waste in the country is increasing at an annual rate of 12 percent, or around two million
tonnes per year. In late January 2022, a leak in the pipeline operated by the Star Petroleum Refining Public Company Ltd caused a spill of 20 to 50 tonnes across 47 km2 of water, with some oil reaching the coast of
Rayong province 20 km away. ==Tourism==