According to Wikipedia, the Pa Sak Jolasid Dam or Pa Sak Cholasit Dam impounds, the Pa Sak River at Ban Kaeng Suea Ten, Tambon Nong Bua, Phatthana Nikhom District, Lopburi Province. It is the biggest reservoir in central Thailand.
The 4,860-metre (15,940 ft) wide and 36.5-metre (120 ft) high dam is earth-filled with an impervious core. The storage capacity is 785 million m3 of water at normal water level, with a maximum capacity of 960 million m3. The dam also supplies about 6.7 MW of hydro-electric power. The Pa Sak Cholasit Dam Project is one of the major irrigation projects of Thailand, providing water to the plantations in the Pa Sak valley and lower Chao Phraya valley. The dam also decreases problems of water management in Bangkok by permitting more flood control, as the Pa Sak river was one of the main sources of flooding in the Bangkok metropolitan area.
King Bhumibol Adulyadej initiated a project to develop the Pa Sak River valley and lower Chao Phraya valley on 19 February 1989 as part of the Maenam Pa Sak Royal Development Project. On 4 July 1991 Prime Minister Anand Panyarachun set up a study group for the dam project. Princess Maha Chakri Sirindhorn presided over a royal ceremony on 15 June 1998, starting the storing of water in the reservoir.
On 20 October 1991 King Bhumibol Adulyadej gave the dam its official name, Pa Sak Cholasit. The king also presided over the inauguration of the dam on 25 November 1999. The park is now also a tourist attraction.