Previously known as Lake Chiew Lan, was responsible for naming the dam Ratchaprapha ('Light of the kingdom'). Located at Ban Chiew Lan in Khao Pang sub-district, construction of the dam was completed in 1988. Covering 165 square kilometers of Surat Thani province, the reservoir area includes over 200 islands within its boundaries and is part of a forest center overseen by Khao Sok National Park.