Pa Sak Jolasid Dam

Pa Sak Jolasid Dam is a large earthfill dam on the Pa Sak River straddling Wang Muang District in Saraburi and Phatthana Nikhom District in Lopburi, central Thailand. Completed in 1999 as a royal initiative of King Bhumibol Adulyadej, it is Thailand's longest dam at 4,860 meters. The dam creates a vast reservoir used for irrigation, flood control and water supply, and is notable for its scenic viewpoint, crest road and seasonal floating railway.

Visitors can expect a vast reservoir surrounded by hills with a long dam crest accessible by road and on foot. The site offers panoramic viewpoints over the water, a visitor exhibition area explaining the dam's construction, landscaped gardens, and a railway line that crosses the reservoir. The area is open and scenic, suitable for sightseeing, photography and leisurely walks along the dam, with food stalls and souvenir shops near the main viewpoint.

Initiated as a royal project of King Bhumibol Adulyadej (Rama IX) to address flooding in the Pa Sak River basin and drought and water shortage in the lower Chao Phraya basin. Construction began in 1994 and was completed in 1999, with official inauguration on 15 June 1999. The dam was built as an earthfill dam with a clay core, 4,860 meters long and 36.5 meters high, creating a reservoir with storage capacity of about 960 million cubic meters for irrigation, water supply and flood mitigation.

Considered a significant royal development project symbolizing water management and agricultural support in central Thailand. The reservoir and dam area is a well-known domestic tourism and recreation site, particularly famous for the seasonal floating railway that has become a cultural tourism attraction.