Pa Sak Jolasid Dam

Pa Sak Jolasid Dam is a large earth-fill dam on the Pa Sak River spanning Phatthana Nikhom District in Lopburi and Wang Muang District in Saraburi, about 150 km northeast of Bangkok. Completed in 1999 as a royal initiative, 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 a popular scenic viewpoint and recreational area.

Visitors can expect a wide, paved dam crest with panoramic views over the large reservoir and surrounding hills. The site includes viewpoint platforms, a landscaped park area at the dam base, and the distinctive railway track that runs across the reservoir. Visitors can walk, cycle or drive along the dam, take photos of the reservoir, visit small exhibition areas about the dam's construction, and during the high-water season see the famous floating train crossing the water.

Initiated as a royal project of King Bhumibol Adulyadej (Rama IX) in 1989 to address flooding in the Chao Phraya basin and drought in the Pa Sak valley. Construction took place from 1994 to 1999 under the Royal Irrigation Department. Inaugurated on 15 June 1999, the dam is an earth-core rockfill structure 4,860 meters long and 36.5 meters high, recognized as Thailand's longest dam, providing irrigation, water supply and flood mitigation.

Represents a major royal water-management initiative valued for supporting agriculture and local livelihoods in Lopburi and Saraburi provinces. The reservoir and dam have become a community recreational area and a seasonal tourism landmark, particularly known for the reservoir railway and annual sunflower viewing in the surrounding countryside.