Kwan Phayao is a lake in Phayao Province, northern Thailand. Kwan, a word from the northern Thai language, means 'lake' or 'large swamp'. The shape of the lake is a nearly-half-circle-moon shape. Phayao Lake is the largest freshwater lake in the northern region and the fourth largest in the country, with a depth of 1.5 metres, and covers an area of about 1,980 hectares. There are about 50 species of fish in Phayao Lake.

Phayao is one of Thailand's seventy-seven provinces (changwat) lies in upper northern Thailand. Neighboring provinces are Nan, Phrae, Lampang, and Chiang Rai. In the northeast it borders Xaignabouli of Laos.