Long-tailed Boat On River Kwai In Kanchanaburi Thailand. Stock Photography

The Khwae Yai River (Thai: แม่น้ำแควใหญ่, RTGS: Maenam Khwae Yai), also known as the Si Sawat is a river in western Thailand. It has its source in the Tenasserim Hills and flows for about 380 kilometres (240 mi) through Sangkhla Buri, Si Sawat, and Mueang Districts of Kanchanaburi Province, where it merges with the Khwae Noi to form the Mae Klong River at Pak Phraek subdistrict. The River Kwai, more correctly Khwae Noi (Thai: แควน้อย) or Khwae Sai Yok (Thai: แควไทรโยค), is a river in western Thailand. It rises to the east of the Salween in the north-south spine of the Bilauktaung range near, but not over the border with Burma. It begins at the confluence of Ranti, Songkalia and Bikhli Rivers. At Kanchanaburi it merges with the Khwae Yai River to form the Mae Klong river, which empties into the Gulf of Thailand at Samut Songkhram.