There's only one Nan River, and it's located entirely in Thailand. It is one of the major tributaries of the Chao Phraya River, the longest river in Thailand. The Nan River originates in the Luang Prabang Range, on the border with Laos, and flows south for about 740 kilometers (460 mi) before joining the Ping River at Nakhon Sawan to form the Chao Phraya River.
The Nan River basin is home to many communities and provides water for irrigation and transportation. The river is also an important source of fish and other aquatic life.