Tropical depression Mulan has dumped a significant amount of rainwater into 35 dams triggering warnings of a potential spillover from some, says the Office of the National Water Resources (ONWR).
Mulan, which has been downgraded from a tropical storm, caused widespread downpours in the upper North and the Northeast from Thursday until Saturday.
This raised levels in waterways across the country, many of which flow into dams. However, authorities warn the danger is not over yet.
Surasee Kittimonthon, the ONWR secretary-general, said on Saturday Mulan has been responsible for increased inflows into 35 dams with a combined capacity of 4,972 million cubic metres of water.
Nine of the 35 dams are located in the North, and have a storage capacity of 2,024 million cubic metres of water.
The ONWR warned some of the dams may be at risk of spilling over and told the Royal Irrigation Department (RID) to watch closely.
A further 12 are in the Northeast with a 1,303 million cubic centimetres of water.
State authorities have been alerted to the rise in water levels in the dams and advised to manage the water outflow to prevent floods in downstream areas, according to Mr Surasee.
Discharging the water from the dams at the appropriate rate is the key to mitigating the impact of storms, he added.
He said the ONWR has told the RID that if more water has to be siphoned from dams, it must tell residents in downstream provinces ahead of time so they can move to higher ground in case of floods.
Six provinces on Saturday remained flooded in the wake of Mulan.
Altogether 1,885 households across 30 districts were inundated although there were no casualties.
Families in the areas most heavily drenched have received help from local administrative organisations as well as the disaster prevention and mitigation offices, and floodwater levels are generally receding, says the Department of Disaster Prevention and Mitigation.
Government spokesman Thanakorn Wangboonkongchana said Prime Minister Prayut Chan-o-cha has been monitoring the situation in the North and Northeast and ordered state agencies to provide assistance urgently.
Gen Prayut has also instructed the armed forces to deploy soldiers in flooded areas where military vehicles and flat-bottomed boats will be used as public transport for residents and help those with special needs.
The military is also cooking meals for residents.
"The situation has to be monitored closely.
"Runoff from the mountains remains a possibility since rain has not let up in many areas," Mr Thanakorn said.
Meanwhile, Bangkok governor Chadchart Sittipunt said areas outside the city's floodwalls such as sections of Rama III Road may be prone to floods.
However the situation in Bangkok is not yet critical.