Pa Sak Jolasid Dam

It is a clay-core earth dam 4,860 m long — billed as Thailand's longest earth dam. Sources give its height as 31.5 or 36.5 m; the crest is at +46.50 m above sea level. It holds 785 million m³ at normal level and 960 million at most, drains 14,520 km² and has a 6.7 MW mini hydro plant. It irrigates the Pa Sak and lower Chao Phraya basins and helps protect Bangkok from floods.

King Bhumibol initiated the Pa Sak basin project on 19 February 1989 after repeated Bangkok floods and named the dam (sources say 20 October 1991 or 7 October 1998). Main construction began on 2 December 1994, impounding started on 15 June 1998, work finished on 30 September 1999, and the King opened it on 25 November 1999. Forty-two villages were moved and 28 archaeological sites flooded. In late September–October 2026 the reservoir was about 96–98% full.

A tram runs along the crest, about 50–60 minutes, to the 14 m white Buddha 'Luang Pu Yai Pa Sak' on the Wang Muang (Saraburi) side, 08:00–16:30, 30 baht adults and 10 children. There is also a royal commemorative tower, the free Pa Sak River Basin Museum (Wed–Sun 08:30–16:30), an aquarium, fish feeding, bicycle hire and a campsite. Near Khok Salung station the railway crosses the reservoir on a causeway that seems to float when the water is high — the origin of the 'floating train'.

The 'floating train' excursion from Bangkok runs in the 2026/27 season on 26 weekend and holiday days from 7 November 2026 to 31 January 2027: 350 baht return in 3rd-class fan, 650 in air-conditioned cars, booked via D-Ticket. It leaves Hua Lamphong at 06:00, stops at the floating-railway viewpoint, reaches the dam about 10:35 and returns by 18:50. Sunflower fields bloom along Highway 21 at the same time. The dam is free with free parking; the crest is sunny and windy with little shade, and lakeside lawns may close at high water. Phone 036-494-291.