Ban Ta Khun is a district in the west of Surat Thani Province of southern Thailand. It is both the largest district of the province and the one with the lowest population density. Most of the district is in the hills of the Phuket Range, with parts being protected within Khao Sok National Park and the Khlong Saeng Wildlife Sanctuary. The main rivers of the district are the Khlong Saeng, which is dammed by the Ratchaprapha dam to form the Cheow Lan reservoir. It empties near the town of Khao Wong into the Phum Duang River. By far the most important reasons for visiting Ban Ta Khun are to visit the dam, take a boat trip around the reservoir or stay on one of the numerous raft houses.