The Ping and Nan rivers merge near the city of Nakhon Sawan to form the Chao Phraya River. The Mae Wong National Park on the border with Khamphaeng Phet province was created in 1987 to preserve the Mae Wong-Mae Poen jungle. Bueng Boraphet is the largest freshwater swamp in Thailand, in total covering 212 km. The swamp is located directly east of the town Nakhon Sawan and extends into the districts Tha Tako and Chum Saeng. During the winter months many waterfowls migrate there. Parts of the swamp are protected as a non-hunting area.