The Khwae Yai River also known as the Si Sawat ( mɛ̂ː náːm sǐː sa.wàt), is a river in western Thailand

Thailand

Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...

. It flows for about 380 kilometres through Sangkhla Buri

Amphoe Sangkhla Buri

Sangkhla Buri is a district in the Kanchanaburi Province in western Thailand.-Geography:Sangkhla Buri is located in the far west of the province, at the boundary to Myanmar. The Three Pagodas Pass is the border crossing station to Myanmar...

, Si Sawat

Amphoe Si Sawat

Si Sawat is a district in the Kanchanaburi Province in western Thailand.- Geography :Neighboring districts are Ban Rai of Uthai Thani Province, Dan Chang of Suphanburi Province, Nong Prue, Bo Phloi, Kanchanaburi, Sai Yok and Thong Pha Phum of Kanchanburi Province.The district is dominated by the...

, and Mueang

Amphoe Mueang Kanchanaburi

Mueang Kanchanaburi is the capital district of Kanchanaburi Province, central Thailand.-History:Mueang Kanchanaburi was changed status to be the capital district of Kanchanaburi province in 1913....

 Districts of Kanchanaburi Province

Kanchanaburi Province

- History :Archaeology found in Kanchanaburi dates back to the 4th century which proves of trade with surrounding countries even in that time. Very little is also historically known about the actual Khmer influence in Kanchanaburi but there is evidence of their occupation with Prasat Muang Singh –...

, where it merges with the Khwae Noi to form the Mae Klong River

Mae Klong

The Mae Klong is a river in western Thailand. The river begins at the confluence of the Khwae Noi or Khwae Sai Yok and the Khwae Yai River or Khwae Si Sawat in Kanchanaburi, pass Ratchaburi Province and empties into the Gulf of Thailand in Samut Songkhram....

 at Pak Phraek subdistrict

Tambon

Tambon is a local government unit in Thailand. Below district and province , they form the third administrative subdivision level. As of the 2009 there are 7255 tambon, not including the 169 khwaeng of Bangkok, which are set at the same administrative level, thus every district contains 8-10 tambon...

.

The famous bridge of the Burma Railway crosses the river at Tha Makham Subdistrict of the Mueang District. However this is not the same bridge as depicted in The Bridge over the River Kwai by Pierre Boulle

Pierre Boulle

Pierre Boulle was a French novelist largely known for two famous works, The Bridge over the River Kwai and Planet of the Apes .-Biography:...

 and in its film adaptation

The Bridge on the River Kwai

The Bridge on the River Kwai is a 1957 British World War II film by David Lean based on The Bridge over the River Kwai by French writer Pierre Boulle. The film is a work of fiction but borrows the construction of the Burma Railway in 1942–43 for its historical setting. It stars William...

. That bridge was built of wood approximately 100 metres upriver from the current bridge. No remnants of the wooden bridge remain.

Up until the 1960s, the river was considered part of the Mae Klong itself, but this part of the Mae Klong was then renamed Khwae Yai to bring geographical fact more in line with the fictional association with the name 'River Kwai'.