Officials increased the discharge rate of the Chao Phraya Dam on Wednesday, sending a huge volume of water downstream.
The release contributed to flooding of villages in the Bang Ban district of Ayutthaya.
Extra water also is being released from the Pasak Jolasid Dam in Lopburi province.
Flood warnings have been issued for five central provinces.
The Chao Phraya Dam in Chai Nat province increased its discharge rate to 2,766 cubic metres of water per second, the highest rate this year.
Somyos Ketsuwan, chief of Bang Ban district, on Wednesday inspected flooded areas adjacent Wat Kopai in tambon Bang Luang Dod after Khlong Bang Luang canal overflowed and flooded four villages there.
A total of 162 households were affected, Mr Somyos said.
Meanwhile, five central provinces have been placed on full alert for rising water as the Pasak Jolasid Dam will also increase its rate of discharge.
The Department of Disaster Prevention and Mitigation on Wednesday sent an urgent letter to the governors of Lop Buri, Saraburi, Ayutthaya, Pathum Thani and Nonthaburi provinces, as well as to directors of provincial disaster prevention agencies, telling them to prepare for discharge from the Pasak Jolasid Dam.
About 515 million cubic metres of runoff was expected to flow into the Pasak Jolasid Dam between Sept 27 and Oct 3. If the discharge rate remained at 8.64 million cubic metres a day, the dam would reach capacity on Sept 30, the RID said.
