Bueng Si Fai (Thai: บึงสีไฟ, pronounced [bɯ̄ŋ sǐː fāj]) is a freshwater lake in central Thailand located in Nai Mueang Subdistrict, Mueang Phichit District, Phichit Province.

Its name is roughly translated as "Fire Mill Marsh" regarded as an important source of freshwater fish breeding and also habitat for variety of birds.

Bueng Si Fai is an oxbow lake by received water flowing from the Nan River.

This lake has a border with four tambons (subdistricts) of Mueang Phichit District, namely Tha Luang, Rong Chang, Khlong Khachen and Mueang Kao.

Nowadays, it is reduced to only 5,390 rai (about 2,094 acres) which is affected by the opening of the Sirikit Dam.