Gulf of Thailand

The Gulf of Thailand, also known as the Gulf of Siam, is a shallow inlet[1][2] in the western part of the South China Sea, a marginal body of water in the western Pacific Ocean. The gulf is around 800 km (497 mi) long and up to 560 km (348 mi) wide, has a surface area of 320,000 km2 (123,553 sq mi) and is surrounded on the north, west and southwest by Thailand, on the northeast by Cambodia and Vietnam. The South China Sea is to the southeast.[3][4]

Gulf of Thailand
Gulf of Siam
Gulf of Thailand
Location of the gulf
LocationSoutheast Asia
Coordinates09°30′N 102°00′E / 9.500°N 102.000°ECoordinates: 09°30′N 102°00′E / 9.500°N 102.000°E
Primary inflowsSouth China Sea
Surface area320,000 km2 (120,000 sq mi)
Average depth58 m (190 ft)
Max. depth85 m (279 ft)


The modern Thai name of the gulf is Ao Thai (Thai: อ่าวไทย,  [ʔàːw tʰāj] (listen), "Thai Gulf") and "Gulf of Thailand" has been adopted as the official name of the body by the International Hydrographic Organization.[5] Its name in Malay and Khmer continues to be the "Gulf of Siam", Teluk Siam and Khmer: ឈូងសមុទ្រសៀម, Chhoung Samut Siem, respectively. In Thai, the gulf is historically known as Ao Sayam (Thai: อ่าวสยาม).[6] In Vietnamese it is known as Vịnh Thái Lan.

It is generally identified with the Great Gulf (Latin: Magnus Sinus) known to Greek, Roman, Arab, Persian, and Renaissance cartographers before the influx of Portuguese explorers removed the phantom Dragon Tail peninsula from European world maps in the 16th century.


Map showing the location of the gulf

The Gulf of Thailand is bordered by Cambodia, Thailand, and Vietnam.[7][8] It occupies a seabed area of 304,000 km2 from 6° N to 13°30' N latitude and 99°E to 104° E longitude.[9]:250 The northern tip of the gulf is the Bay of Bangkok at the mouth of the Chao Phraya River. The southern boundary of the gulf is defined by a line from Cape Bai Bung in southern Vietnam (just south of the mouth of the Mekong River) to the city of Kota Bharu on the Malaysian coast.

The gulf is relatively shallow: its mean depth is 58 metres (190 ft) and the maximum depth is only 85 metres (279 ft).[9]:250 This makes water exchange slow, and the strong water inflow from the rivers reduce the level of salinity in the gulf (3.05–3.25 percent) and enriches the sediments. Only at greater depths does water with a higher salinity (3.4 percent) flow into the gulf from the South China Sea. It fills the central depression below a depth of 50 metres (160 ft). The main rivers which empty into the gulf are the Chao Phraya, including its distributary Tha Chin River, the Mae Klong, and Bang Pakong rivers at the Bay of Bangkok, and to a lesser degree the Tapi River flowing into Bandon Bay in the southwest of the gulf.

The International Hydrographic Organization defines the southern limit of the gulf as "[a] line running from the Western extreme of Cambodia or Camau Point (8°36'N) to the Northern extreme of the point on the East side of the estuary of the Kelantan River (6°14′N 102°15′E / 6.233°N 102.250°E)".[5]

Seabed morphology

The seabed morphology in the central depression of the gulf is characterised by the presence of elongated mounds and ridges arranged parallel to the axis of the basin. This morphology, widespread within the gulf in water depths exceeding 50 m, covers an area of tens of thousands of square kilometres.

It reflects an interaction between sediment dewatering and the erosional activity of the present-day bottom currents.[10] The sediment dewatering and fluid seepage result in the formation of numerous small pits and pockmarks. The long-term erosion imposed by currents of stable orientation modifies pockmarks into long runnels and depressions, and ultimately leads to the formation of the large fields of elongated mounds and ridges, as well as the residual outliers of un-eroded mud and clay sheets.[10]


  • Vinh Tuan Ven
  • Vinh Ba Hon
  • Vinh Hon Chong


The larger islands in the gulf include:


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.[11] In 2016, coral bleaching was detected at Ko Thalu and Ko Lueam in Prachuap Khiri Khan Province for the first time.[12] 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.[13]

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.[14]:52 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.[14]:54 Songkhla was the only province on the gulf with coastal water rated "good" quality.[14]:56


Of Thailand's total marine catch, 41 percent is caught in the Gulf of Thailand and 19 percent in the Andaman Sea. Forty percent is caught in waters outside Thailand's EEZ.[11]

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.[15]

Plastic pollution

In February 2017, a 10 kilometer-long patch of plastic refuse was found floating off Chumphon Province.[16] 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.[17]

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.[16] Filter feeding invertebrates tested off the coast of Chonburi Province showed high levels of microplastics, leading the authors to warn that, "Health risks are possible when people consume these contaminated marine organisms, particularly shellfish."[18]

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.[16]


Eden's whale feeds in the gulf
Bryde's whale (9547580674)
Eden's whale off Bang Tapun.

The gulf's many coral reefs have made it attractive to divers. The tropical warmth of the water attracts many tourists. Some of the most important tourist destinations in the Gulf of Thailand are the islands of Ko Samui and Ko Pha Ngan in Surat Thani Province, Pattaya in Chonburi Province, Cha-am in Phetchaburi Province, Hua Hin in Prachuap Khiri Khan Province, and Ko Samet in Rayong Province.

In recent years, the bay has become known for its whale watching activities, targeting the endemic, critically endangered populations of cetaceans (Eden's whales, newly described Omura's whales, Chinese white dolphins, and Irrawaddy dolphins showing unique feeding behaviors), and dugongs.[19][20][21] It was first classified by Müller in 1776 as Trichechus dugon.[22] Presence of a critically endangered Hawksbill sea turtle, a rare species in Thai waters, was confirmed during whale watching expeditions in January, 2016.[23]

Territorial disputes

The area between Malaysia, Thailand, Cambodia, and Vietnam is subject to several territorial disputes. Malaysia and Thailand have chosen to jointly develop the disputed areas, which include the islands of Ko Kra and Ko Losin.[24] A long-standing dispute between Cambodia and Vietnam in the Gulf of Thailand concerns mainly the island of Phú Quốc or Koh Tral in Khmer, which is off the Cambodian coast.[25] Cambodia also claims 48,000 square kilometres (19,000 sq mi) of shelf area.[26][27]

See also


  1. ^ "Marine Gazetteer browser". Marineregions org. Retrieved June 6, 2016.
  2. ^ "Thailand, Gulf of". Oxford University Press. Retrieved June 6, 2016.
  3. ^ "Marine Gazetteer Placedetails - Gulf of Thailand". Marineregions org. Retrieved June 6, 2016.
  4. ^ "Gulf of Thailand". Retrieved June 7, 2016.
  5. ^ a b "Limits of Oceans and Seas" (PDF) (3 ed.). International Hydrographic Organization. 1953. p. 23. Retrieved 7 February 2010.
  6. ^ ระยะทางเสด็จฯ ประพาสชายทะเลอ่าวสยาม พ.ศ. 2470 [A report on the royal travel through the Gulf of Siam, 1927] (pdf). Royal Thai Government Gazette (in Thai). 88 (D): 44. 1927-05-22. Retrieved 2014-03-08.
  7. ^ "Map of Gulf of Thailand, Gulf of Thailand Location Facts, Major Bodies of Water, South China Sea". World Atlas. Retrieved 29 July 2018.
  8. ^ "Gulf of Thailand". Encyclopedia Britannica. Retrieved 29 July 2018.
  9. ^ a b Khongchai, Narongsak; Vibunpant, Somchai; Eiamsa-ard, Monton; Supongpan, Mala. "Preliminary Analysis of Demersal Fish Assemblages in Coastal Waters of the Gulf of Thailand" (PDF). Worldfish. Archived from the original (PDF) on 19 February 2015. Retrieved 19 Feb 2015.
  10. ^ a b Puchala, R. (2014), Morphology and origin of modern seabed features in the central basin of the Gulf of Thailand, doi:10.13140/RG.2.1.3891.0808
  11. ^ a b Oceans in the Balance, Thailand in Focus (PDF). Bangkok: Greenpeace Southeast Asia (Thailand). c. 2012. Retrieved 11 July 2017.
  12. ^ Wipatayotin, Apinya (2016-04-04). "Rising sea temps bring coral bleaching to Gulf". Bangkok Post. Retrieved 4 April 2016.
  13. ^ Rujivanarom, Pratch (2018-05-29). "More coral reefs damaged by mass bleaching". The Nation. Retrieved 2 June 2018.
  14. ^ a b c Thailand State of Pollution Report 2015 (PDF). Bangkok: Pollution Control Department, Ministry of Natural Resources and Environment (Thailand). 2016. ISBN 978-616-316-327-1. Retrieved 5 September 2017.
  15. ^ Wipatayotin, Apinya (10 December 2017). "Shoring up defences". Bangkok Post Spectrum. 10 (50). Retrieved 10 December 2017.
  16. ^ a b c Wonggruang, Piyaporn (6 May 2018). "SPECIAL REPORT: Alarm raised as Thailand drowns in plastic trash". The Nation. Retrieved 6 May 2018.
  17. ^ Stemming the Tide: Land-based strategies for a plastic- free ocean (PDF). Ocean Conservancy-McKinsey Center for Business and Environment. September 2015. p. 3. Retrieved 6 May 2018.
  18. ^ Thushari, GGN; Senevirathna, JDM; Yakupitiyage, A; Chavanich, S (2017-11-15). "Effects of microplastics on sessile invertebrates in the eastern coast of Thailand: An approach to coastal zone conservation". Marine Pollution Bulletin. 124 (1): 349–355. doi:10.1016/j.marpolbul.2017.06.010. PMID 28760587. Retrieved 6 May 2018.
  19. ^ "Dugongs and seagrass in Thailand: Present status and future challenges" (PDF). Phuket Marine Biological Center and Department of Marine and Coastal Resources. pp. 41–50. Retrieved June 7, 2016.
  20. ^ "Conservation of the Dugong (Dugong Dugon) on the Eastern Coast of the Gulf of Thailand" (PDF). Ocean Park Conservation Foundation Aberdeen, Hong Kong & Project Aware, Australia. May 1, 2004. Retrieved June 7, 2016.
  21. ^ Marsh, H. et al. (2002). Dugong: status reports and action plans for countries and territories Archived 2007-05-08 at the Wayback Machine.. IUCN.
  22. ^ Dugong dugon. The Paleobiology Database. Retrieved on 22 July 2007.
  23. ^ "Wild Encounter Thailand". Retrieved 16 March 2018.
  24. ^ "Defining areas for joint development in disputed waters - Malaysia–Thailand p. 13". University of Wollongong. Retrieved June 7, 2016.
  25. ^ Prescott, J. R. V. (1978). Boundaries and Frontiers. Rowman and Littlefield. ISBN 978-0847660865.
  26. ^ Paul Ganster & David E. Lorey, Borders and border politics in a globalizing world.
  27. ^ Schofield, Clive (2008). "Maritime Claims, Conflicts and Cooperation in the Gulf of Thailand". Ocean Yearbook Online. 22: 75–116. doi:10.1163/221160008x00064.

External links

Chachoengsao Province

Chachoengsao (Thai: ฉะเชิงเทรา, pronounced [t͡ɕʰàʔ.t͡ɕʰɤ̄ːŋ.sāw]) is a province (changwat) of Thailand. Neighboring provinces are (from north clockwise) Prachin Buri, Sa Kaeo, Chanthaburi, Chon Buri, Samut Prakan, Bangkok, Pathum Thani, and Nakhon Nayok. It has a short coastline on the Gulf of Thailand.

Chanthaburi Province

Chanthaburi (Thai: จันทบุรี, pronounced [t͡ɕān.tʰáʔ.bū.rīː]; Chong: จันกะบูย, chankabui, lit: 'Lady Chan, Who wears a pan on her head') is a province (changwat) of Thailand. It is in the east of Thailand, on the border with Battambang and Pailin of Cambodia, on the shore of the Gulf of Thailand. Neighbouring provinces are Trat in the east and Rayong, Chonburi, Chachoengsao, and Sa Kaeo to the west and north.

Chonburi Province

Chonburi (Thai: ชลบุรี, RTGS: Chon Buri, [tɕ͡ʰōn bū.rīː] (listen)) is an eastern province (changwat) of Thailand. Neighboring provinces are (from north clockwise) Chachoengsao, Chanthaburi, and Rayong. To the west is the Gulf of Thailand. Chonburi is home to Thailand's largest tourist-oriented city, Pattaya (also spelled Phatthaya). It is home to Thailand's largest and primary seaport. Due to these factors, the province's population is growing rapidly, with currently some 1.7 million residents (albeit with a large floating or unregistered population). The registered population as of 31 December 2012 was 1.36 million.

Chumphon Province

Chumphon (Thai: ชุมพร, pronounced [t͡ɕʰūm.pʰɔ̄ːn]) is a southern province (changwat) of Thailand on the Gulf of Thailand. Neighbouring provinces are Prachuap Khiri Khan, Surat Thani, and Ranong. To the west it borders the Burmese province of Tanintharyi.

Cà Mau Province

Cà Mau (listen) is a province of Vietnam, named after its capital city. It is located in the Mekong Delta of southern Vietnam, and is the southernmost of Vietnam's 58 provinces. It is bordered on the north by Kiên Giang and Bạc Liêu provinces, on the west by the Gulf of Thailand, and to the south and east by the South China Sea.

Kampot Province

Kampot (Khmer: ខេត្តកំពត IPA: [kɑmpɔːt]) is a (south west province) province (khaet) of Cambodia. It borders the provinces of Koh Kong and Kampong Speu to the north, Takeo and Kep and Vietnam to the east and Sihanoukville to the west. To its south it has a coastline of around 45 km on the Gulf of Thailand. It is rich in low arable lands and has abundant natural resources. Its capital is Kampot town.

Kampot Province had a population of 627,884 in 2010 and consist of eight districts divided into 92 communes with a total of 477 villages. Touk Meas City is located in Kampot Province.

Kiên Giang Province

Kiên Giang (listen) is a province of Vietnam, located in the Mekong Delta region of southern Vietnam. It is known for fishing and rice farming. The provincial capital is Rạch Giá, 250 km from the Ho Chi Minh City. Kiên Giang's dimension is about 6,299 km² and its population is about 1,634,043, of which 22 percent live in the urban area.

Kiên Giang is bordered with An Giang Province in the northeast, Cần Thơ and Hậu Giang in the east, Bạc Liêu in the southeast and Cà Mau in the south, and Kampot Province of Cambodia (with the 54 km border) in the west, Gulf of Thailand in the southwest (with the 200 km coast).

According to survey results in April 1, 2009, Kiên Giang province's population is 1,683,149 people.

Koh Kong Province

Koh Kong (Khmer: ខេត្តកោះកុង; IPA: [kɑh koŋ], "Kong Island") is a province (khaet) of Cambodia. The name means "Kŏng Island Province". Its capital is Khemarak Phoumin. The province was called Patchanta Khiri Khet (Thai: ปัจจันตคิรีเขตร; Thai pronunciation: [pàt.tɕan.tàʔ kʰi.riː.kʰèːt]) from 1795 to 1904.

Kra Isthmus

The Kra Isthmus (Thai: คอคอดกระ, pronounced [kʰɔ̄ː kʰɔ̂ːt kràʔ]; Malay: Segenting Kra/Segenting Kera) is the narrowest part of the Malay Peninsula, in southern Thailand.

Narathiwat Province

Narathiwat (Thai: นราธิวาส, pronounced [nā.rāː.tʰí.wâːt]) is one of the southern provinces (changwat) of Thailand. Neighboring provinces are (from west clockwise) Yala and Pattani. To the south it borders the Malaysian state of Kelantan. The southern railway line ends in this province, which is one of the nation's four provinces that border Malaysia. The province features a range of cultures as well as natural resources, and is relatively fertile. Narathiwat is about 1,140 kilometers south of Bangkok and has an area of 4,475 square kilometers. Seventy-five percent of the area is jungle and mountains and has a tropical climate.

Pattani Province

Pattani (Thai: ปัตตานี, pronounced [pàt.tāː.nīː]) is one of the southern provinces (changwat) of Thailand. Neighboring provinces are (from southeast clockwise) Narathiwat, Yala, and Songkhla.

Phetchaburi Province

Phetchaburi (Thai: เพชรบุรี, pronounced [pʰét.t͡ɕʰā.bū.rīː]) or Phet Buri (pronounced [pʰét bū.rīː]) is one of the western or central provinces (changwat) of Thailand. Neighboring provinces are (from north clockwise) Ratchaburi, Samut Songkhram, and Prachuap Khiri Khan. In the west it borders the Tanintharyi Division of Myanmar. Phetchaburi has a national park called "Kaeng Krachan" which consists of a reservoir overlooking its islands.

Phú Quốc

Phú Quốc (Vietnamese: [fǔ wək]), is the largest island in Vietnam. Phú Quốc and nearby islands, along with distant Thổ Chu Islands, is part of Kiên Giang Province as Phú Quốc District, the island has a total area of 574 square kilometres (222 sq mi) and a permanent population of approximately 103,000. Located in the Gulf of Thailand, the district of Phú Quốc includes the island proper and 21 smaller islets. Dương Đông town, is located on the west coast, and is also the administrative and largest town on the island. The other township is An Thoi on the southern tip of the island.

The economy is centred on fishing, agriculture and a fast-growing tourism sector. Phu Quoc has achieved fast economic growth due to its current tourism boom. Many infrastructure projects have been carried out, including several five-star hotels and resorts. Phu Quoc International Airport is the hub connecting Phú Quốc with mainland Vietnam and other international destinations.

From March 2014, Vietnam allows all foreign tourists to visit Phú Quốc visa-free for a period of up to 30 days. By 2017, the government of Vietnam is planning to set up a Special Administrative Region which covers Phu Quoc Island and peripheral islets and upgrades it to a provincial city with special administration.

Rayong Province

Rayong Province (Thai: ระยอง, pronounced [rā.jɔ̄ːŋ]; Chong: ราย็อง) is a province (changwat) of Thailand. Neighboring provinces are (from west clockwise) Chonburi, and Chanthaburi. To the south is the Gulf of Thailand.

Samut Prakan Province

Samut Prakan (Thai: สมุทรปราการ, pronounced [sāmùt prāːkāːn] (listen)) is one of the central provinces (changwat) of Thailand, established by the Act Establishing Changwat Samut Prakan, Changwat Nonthaburi, Changwat Samut Sakhon and Changwat Nakhon Nayok, Buddhist Era 2489 (1946), which came into force 9 March 1946.

It is part of the Bangkok Metropolitan Region. Neighbouring provinces are Bangkok, to the north and west, and Chachoengsao to the east.

Suvarnabhumi Airport is in the Bang Phli District of Samut Prakan Province.

Samut Sakhon Province

Samut Sakhon (Thai: สมุทรสาคร, pronounced [sā.mùt sǎː.kʰɔ̄ːn]) is one of the central provinces (changwat) of Thailand, established by the Act Establishing Changwat Samut Prakan, Changwat Nonthaburi, Changwat Samut Sakhon, and Changwat Nakhon Nayok, Buddhist Era 2489 (1946), which came into force on March 9, 1946.

Neighboring provinces are (from the southwest clockwise) Samut Songkhram, Ratchaburi, Nakhon Pathom, and Bangkok.

It is part of the Bangkok Metropolitan Region.

Samut Songkhram Province

Samut Songkhram (Thai: สมุทรสงคราม, pronounced [sā.mùt sǒŋ.kʰrāːm]) is one of the central provinces (changwat) of Thailand.

Neighbouring provinces are (from the south clockwise) Phetchaburi, Ratchaburi and Samut Sakhon. Local people call Samut Songkhram Mae Klong. The province is the smallest in area of all Thai provinces. Chang and Eng Bunker, the famous Siamese twins were born here on 11 May 1811.

Songkhla Lake

Songkhla Lake (Thai: ทะเลสาบสงขลา, RTGS: Thale Sap Songkhla, IPA: [tʰa.leː sàːp sǒŋ.kʰlǎː]) is the largest natural lake in Thailand. It is on the Malay peninsula in the southern part of the country. Covering an area of 1,040 km2 it borders the provinces of Songkhla and Phatthalung. Despite being called a lake, this water feature is actually a lagoon complex geologically.

The lake is divided into three distinct parts. The southern part opens with a 380 m wide strait to the Gulf of Thailand at the city of Songkhla. Here it contains brackish water about half the salinity of seawater. Further north, after a narrowing to 6 km width, is the Thale Luang (782.80 km2). At the northern end between mangrove swamps is the 28 km2 Thale Noi in Phatthalung Province. The most striking feature is the long 75 km long spit which separates the lake from the sea. Unlike most spits, it was probably formed when originally existing islands were connected by silting from the lake precursor.

Surat Thani Province

Surat Thani (Thai: สุราษฎร์ธานี, pronounced [sù.râːt tʰāː.nīː]), often shortened to Surat, is the largest of the southern provinces (changwat) of Thailand. It lies on the western shore of the Gulf of Thailand. Surat Thani means "city of good people", a title given to the city by King Vajiravudh (Rama VI).

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