Written evidence of the river being referred to by the nameChao Phraya dates only to the reign of KingMongkut (Rama IV, 1850–1868). It is unknown what name, if any at all, was used for the river in older times.[6] The river was likely known simply by the Thai word for 'river',แม่น้ำ (RTGS: mae-nam), and foreign documents and maps, especially by Europeans visiting during theAyutthaya period, usually named the river theMenam.[7][b]
The name Chao Phraya likely comes fromBang Chao Phraya (บางเจ้าพระยา), an alternative name, documented from around 1660 in the reign of KingNarai, of the settlement that is nowSamut Prakan. Historian Praphat Chuvichean suggests that the name, which is atitle of nobility, originated from the story of two Khmer idols being unearthed in 1498 at the settlement that was by the mouth of the river at the time. When the delta extended further into the sea, a new settlement was founded to guard the new river mouth, and the new settlement probably gained the name Bang Chao Phraya (bang being a common term for village names) as a reference to the memory of the idols.[10] There are references in records from the time of KingBorommakot (r. 1733–1758) toPak Nam Bang Chao Phraya (ปากน้ำบางเจ้าพระยา,pak nam meaning 'river mouth'), suggesting that the name had become attached to the mouth of the river by that time,[6] and later became used for the entire river.[10]
In the English-language media in Thailand, the name Chao Phraya River is often translated asriver of kings.[11]
On the basins of Chao Phraya River rose the earliest civilizations in the southeast Asia, most notably the ancient Mon kingdom and the civilization ofDvaravati from the 7th century to the 11th century. The river played a crucial role in theLavo kingdom that existed on its left bank in the Upper Chao Phraya valley and then maintained its role in the kingdoms that succeeded the Lavo kingdom. It formed the basis of the Ayodhya Kingdom, which was later incorporated into theAyutthaya Kingdom in the 14th century, which itself was the precursor of modern Thailand (known formerly as Siam). The river became very significant after the establishment of Rattanakosin (Bangkok) in 1782 on its east bank, the location of Bangkok on the east bank of Chao Phraya River ensuring protection for Siam from the Burmese invasions coming from the west.
Chao Phraya River in Siam (Ayutthaya) Map by Valentijn 1726
In the lowalluvial plain which begins below theChao Phraya Dam, there are many small canals (khlong) that split off from the main river. Thekhlongs are used for the irrigation of the region's rice paddies.
The rough coordinates of the river are 13 N, 100 E. This area has a wet monsoon climate, with over 1,400 millimetres (55 in) of rainfall per year. Temperatures range from 24 to 33 °C (75 to 91 °F) in Bangkok.
The lower Chao Phraya underwent several human-made modifications during theAyutthaya period. Several shortcut canals were constructed to bypass large loops in the river, shortening the trip from the capital city to the sea. The course of the river has since changed to follow many of these canals.
In 1538, Thailand's firstriver engineering of a 3 km (2 mi) long canal was dug at the order ofKing Chairachathirat. It was called "Khlong Lat", and today forms a part ofKhlong Bangkok Noi. It shortened the route by 13–14 km for ships from the Gulf of Siam to the then-capital city,Ayutthaya.[12]
In 1542, a two-kilometer-long canal, "Khlong Lat Bangkok", was completed. The Chao Phraya then diverted along the new canal, its old course becoming part of Khlong Bangkok Noi andKhlong Bangkok Yai. It is said to have shortened the river route by 14 km (9 mi).[12]
In 1608, a seven-kilometer-long "Khlong Bang Phrao" canal was completed and has shortened the Chao Phraya's original route by 18 km (11 mi).[12]
In 1636, the "Khlong Lat Mueang Nonthaburi" was completed.[12]
In 1722, the two-kilometre long "Khlong Lat Kret Noi" shortened the Chao Phraya by 7 km (4 mi). This route formed the island ofKo Kret.[12]
In 2024 the 22-km-long "Chao Phraya II" channel was under construction. It will join the river at points to the north and south of Ayutthaya, providing flood relief for the city.[13]
Major bridges cross the Chao Phraya in Bangkok: theRama VI railroad bridge;Phra Pin-klao near theGrand Palace;Rama VIII, a single tower asymmetrical cable-stayed bridge;Rama IX, a semi-symmetric cable-stayed bridge; andMega Bridge, on the Industrial Ring Road.
In Bangkok, the Chao Phraya is a major transportation artery for a network of river buses, cross-river ferries, and water taxis ("longtails"). More than 15 boat lines operate on the rivers and canals of the city, includingcommuter lines.
The principal tributaries of the Chao Phraya River are thePa Sak River, theSakae Krang River, theNan River (along with its principal confluent theYom River), thePing River (with its principal confluent, theWang River), and theTha Chin River.[14][15][16] Each of these tributaries (and the Chao Phraya itself) is augmented by minor tributaries referred to askhwae. All of the tributaries, including the lesser khwae, form an extensive tree-like pattern, with branches flowing through nearly every province in central and northernThailand.[14] None of the tributaries of the Chao Phraya extend beyond the nation's borders.[17] The Nan and the Yom River flow nearly parallel fromPhitsanulok to Chumsaeng in the north of Nakhon Sawan Province. TheWang River enters the Ping River near Sam Ngao district inTak Province.
When measured from the most commonly accepted source, which is the confluence of the Ping and Nan River in Nakhon Sawan, the river measures 372 km (231 mi). However, when measured from the longest source, which is the origin point of the Nan River in theLuang Prabang Range, the river measures 1,112 km (691 mi).
The expanse of the Chao Phraya River and its tributaries, i.e., the Chao Phraya river system, together with the land upon which falling rain drains into these bodies of water, form the Chao Phrayawatershed.[18]
The Chao Phraya watershed is the largest watershed in Thailand, covering approximately 35 percent of the nation's land, and draining an area of 157,924 square kilometres (60,975 sq mi).[19]
The watershed is divided into the following basins:
Tha Chin Basin (the basin of the Chao Phraya's most significant distributaries)
Finally the Chao Phraya Basin itself is defined as the portion of the Chao Phraya watershed drained by the Chao Phraya River itself, and not by its major tributaries or distributaries. As such, the Chao Phraya Basin drains 20,126 square kilometres (7,771 sq mi) of land.[19]
To the west, the central plain of Thailand is drained by theMae Klong and the east by theBang Pakong River. They are not part of the Chao Praya system.
The landscape of the river basins is a very wide, flat, well-watered plain continuously refreshed with soil and sediment brought down by the rivers. The lower central plain from the delta north toAng Thong Province is a flat, low area with an average of two metres above sea level. Further north and into the plains of the Ping and the Nan the elevation is over 20 m. Then the mountains that are the natural boundary of the Chao Praya watershed form adivide, which has, to some degree, historically isolated Thailand from other Southeast Asian civilisations. In northern Thailand, the divide roughly corresponds to a long section of the political border of the country today. Southern portions of the divide's boundary correspond less to the nation's political border because isolation in this area was prevented by the ease of transportation along the lowlands surrounding the Gulf of Thailand, allowing a unified Thai civilisation to extend beyond the watershed without issue. The slightly higher northern plains have been farmed for centuries and saw a major change from the 13th century during theSukhothai Kingdom in the 13th and 14th centuries and theAyutthaya Kingdom that succeeded it when rice growing intensified with the introduction offloating rice, a much faster-growing strain of rice fromBengal. The southern swamps meanwhile changed radically from the 18th century when KingBuddha Yodfa Chulaloke moved the capital of Siam to Bangkok, and a process of canalisation and cultivation began, especially as Thailand began to export rice from 1855.
TheTha Chin River is the major distributary of the Chao Phraya River. The expanse of the Chao Phraya andTha Chin Rivers and their distributaries, starting at the point at which the distributaries diverge, together with the land amid the triangle formed by the outermost and innermost distributary, form the Chao PhrayaDelta. The many distributaries of the Chao Phraya delta are interconnected by canals that serve both for irrigation and transportation.
The original swamp forests have almost entirely been removed as the plain has been converted to rice paddies, other agriculture, and urban areas like Bangkok. Much of the wildlife that once inhabited these plains has disappeared, including a large number of fish in the river systems, birds such as vultures, theOriental darter (Anhinga melanogaster),white-eyed river martin (Pseudochelidon sirintarae), thesarus crane (Grus antigone)[21] and animals such astigers,Asian elephants,Javan rhinoceroses, and the much-huntedSchomburgk's deer.[22] Today we can only guess at the original habitat and wildlife by comparing it with neighbouring countries. It is believed that the area would have consisted of freshwater swamps inland and saltymangroves on the coast and river estuaries. The swamp would have been covered inPhragmites marsh grasses. Today there is a small area of this remaining inKhao Sam Roi Yot National Park, a relic of the original landscape.
As so much has been cleared or altered the potential for creating large protected areas to preserve original habitat no longer exists. However much wildlife does remain in the rice fields and steps may be taken to preserve these as urban and industrial development on the plains is ongoing and theIndustrial Estate Authority of Thailand has very little control or planning over this. Particular threats come from the conversion of rice paddies to large-scale production of prawns by pumping in seawater, and the use of pesticides to eliminate the introduced snail,Pomacea canaliculata, which damages rice plants.
There are populations of threatened birds, including colonies of breeding water birds such as the world's largest populations of the near-threatenedAsian openbill (Anastomus oscitans), and other birds such as the winteringblack kite (Milvus migrans). Endemic mammals that remain are thelimestone rat (Niviventer hinpoon),Neill's long-tailed giant rat (Leopoldamys neilli), and the near-endemicThailand roundleaf bat (Hipposideros halophyllus).
Thegiant barb is one of the world's largest freshwater fish weighing up to 300 kg (660 lb),[24] but the natural population has beenextirpated from Chao Phraya.[25]
The Chao Phrayabasin is home to around 280 species of fish, including about 30endemics.[26] By far the most diverse family isCyprinidae with 108 species.[26] The mainstream of the Chao Phraya River has about 190 native fish species.[23] In general, the aquatic fauna of Chao Phraya andMae Klong show clear similarities, and they are sometimes combined in a singleecoregion with 328 fish species.[23] Despite their similarities, there are also differences between the aquatic fauna of Chao Phraya and Mae Klong; the latter (but not the former) is home to a fewtaxa otherwise only known in majorBurmese rivers: theIrrawaddy,Salween, andTenasserim.[23] The aquatic fauna in Chao Phraya–Mae Klong also show clear similarities with that of the middleMekong (the lower Mekong fauna more closely resembles that of the easternMalay Peninsula).[23] It is believed that the upper Mekong was connected to Chao Phraya (rather than the present-day lower Mekong) until theQuaternary, which explains the similarities in their river faunas. This included theNan River basin, a tributary of the Chao Phraya, which is home to several taxa (for example,Ambastaia nigrolineata andSectoria) otherwise only known from Mekong.[23] Of the fish species known from the Chao Phraya–Mae Klong, only about 50 are absent from the Mekong.[23]
The only remaining wild population of thered-tailed black shark is restricted to an area of less than 10 km2 (4 sq mi).[27]
There has been extensive habitat destruction (pollution,dams, anddrainage forirrigation) in the Chao Phraya basin andoverfishing also presents a problem.[23][28][29][30] Withinmainland Southeast Asia, the only freshwater region with similar high levels of threat is the lower Mekong.[23] It has been estimated that only around 30 native fish species still can reproduce in the mainstream of the Chao Phraya River.[23]
The catfishPlatytropius siamensis is endemic to Chao Phraya andBang Pakong, but has not been recorded since the 1970s and is consideredextinct.[31] Recent records of the near-endemic cyprinidBalantiocheilos ambusticauda are also lacking and it is possibly extinct.[23][32] Three of thelargest freshwater fish in the world are native to the river, but these are all seriously threatened: the critically endangeredgiant barb (wild populations have beenextirpated from Chao Phraya, but remain elsewhere),[25] critically endangeredgiant pangasius,[33] and endangeredgiant freshwater stingray.[34] The critically endangeredred-tailed black shark, a small colourful cyprinid that is endemic to Chao Phraya, is commonly seen in the aquarium trade where it is bred in large numbers, but the only remaining wild population is at a single location that covers less than 10 km2 (4 sq mi).[27] The endangereddwarf loach, another species bred in large numbers for the aquarium trade, has been extirpated from most of its range in Chao Phraya.[35] The critically endangeredSiamese tigerfish has been entirely extirpated from Chao Phraya and Mae Klong, but small populations remain in the Mekong basin.[36]
Basa fish from the Chao Phraya and Mekong is an important food fish, and it is alsofarmed.[37]
The Thai Pollution Control Department (PCD) reports that thewater quality of major rivers flowing into the upperGulf of Thailand has seriously deteriorated, and the lower Chao Phraya contains bacteria andnutrient pollution fromphosphates,phosphorus, andnitrogen. Nutrient pollution causesalgae to grow faster than ecosystems can handle, harming water quality, food resources for aquatic animals, and marine habitats. It also decreases the oxygen that fish need to survive. PCD rated water quality at the mouth of Chao Phraya in Bangkok'sBang Khun Thian District as "very poor", worse than in 2014, and their findings indicated large amounts of wastewater were discharged into the river from households, industry, and agriculture.[39][40] In addition, 4,000 metric tons of plastic flow down the river into the Gulf of Thailand every year. To counter this, Thailand's Department of Marine and Coastal Resources (DMCR) signed an agreement withThe Ocean Cleanup organization to deploy an Interceptor Original, one of the organization's solar-powered, automated systems, in the river. Since 19 February 2024, an interceptor of the latest third generation has been deployed for testing purposes.[41][42]
^Irishsurveyor andcartographerJames McCarthy,F.R.G.S., who served as Director-General of the Siamese Government Surveys prior to establishment of theRoyal Thai Survey Department, wrote in his account, "Me Nam is a generic term,Me signifying "mother," andNam "water," and the epithet Chao P'ia signifies that it is the chief river in the kingdom of Siam."[5]Herbert Warington Smyth, who served as Director of the Department of Mines in Siam from 1891 to 1896,[8] refers to it in his book first published in 1898 as "the Mae Nam Chao Phraya".[9]
^Kannika Suteerattanapirom (2022).Bōrānnakhadī Krung Thon Burīโบราณคดีกรุงธนบุรี (in Thai). Bangkok: Matichon.ISBN978-974-02-1813-5. Excerpt in"ย้อนร่องรอยแม่น้ำเจ้าพระยาในอดีต..."Matichon Book Facebook page. Matichon. 27 December 2022. Retrieved2 June 2025.
^Tamara Loos (1 December 2002)."Introduction to Five Years in Siam".1994 reprint. Pine Tree Web. Archived fromthe original on 19 December 2010. Retrieved1 March 2011.At the time of writing the "Introduction" to the 1994 reprint of Five Years in Siam, she was a PhD candidate in the Department of History at Cornell University.
^abPraphat Chuvichean (25 May 2016). "บางเจ้าพระยา ชื่อเก่าก่อนแม่น้ำเจ้าพระยา". Thongthin Mi Chumchon.Siam Rath Daily (in Thai). Quoted inSujit Wongthes (16 June 2016).""เจ้าพระยา" ในชื่อแม่น้ำเจ้าพระยา ได้จากเทวรูปขอม".Matichon Online (in Thai). Retrieved2 June 2025.
^Samorn Muttamara, S. & Sales, C. L. (1994).Water quality management of the Chao Phraya River (a case study). Environmental Technology 15(6).
^Molle, F. (2005).Elements for a political ecology of river basins development: The case of the Chao Phraya river basin, Thailand. Paper presented to the 4th Conference of the International Water History Association, December 2005, Paris.
^Chuenpagdee, R.; Traesupap, S. & Juntarashote, K. (2010).Coastal Transect Analysis of Chao Phraya Delta, Thailand. pp. 398-407 in: Hoanh, C.T. & Szuster, B.W. (editors).Tropical Deltas and Coastal Zones: Food Production, Communities and Environment at the Land-water Interface.ISBN9781845936181.
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