His Majesty the King has presided over a ceremony to officially open a royal project initiated by the late King Bhumibol in Prachin Buri.
The King travelled to the province's Na Di district on Sunday to open Naruebodindrachinta Reservoir, used for irrigation and flood prevention.
The reservoir can hold up to 295 million cubic metres of water fed by the Prachin Buri River, and can both prevent flooding in areas downstream and channel water to farmers during the dry season.
The reservoir can release water to prevent saline intrusion from the Gulf of Thailand into the Bang Pakong River.
The Prachin Buri is a tributary of the Bang Pakong.
Provincial governor Suriya Amornrotworawut has praised the late King for his vision to help people who rely on water from the Prachin Buri River.
Naruebodindrachinta Reservoir was called Huay Samong before the late King renamed it last year.