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| Khwae Yai River | |
|---|---|
 The bridge of the Burma Railway crosses the river at the town of Kanchanaburi. | |
 | |
| Native name | แม่น้ำแควใหญ่ (Thai) |
| Location | |
| Country | Thailand |
| Physical characteristics | |
| Source | |
| • location | Umphang District |
| Mouth | |
• location | Kanchanaburi |
| Length | 380 km |
| Basin features | |
| River system | Mae Klong |
The Khwae Yai River (Thai: แม่น้ำแควใหญ่, RTGS: Maenam Khwae Yai, IPA: [mɛ̂ːnáːm kʰwɛː jàj]), also known as the Si Sawat (แม่น้ำศรีสวัสดิ์ [mɛ̂ː náːm sǐː sa.wàt]), 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.