Agriculture and Cooperatives Minister Chalermchai Sri-on has ordered the Royal Irrigation Department to install more pumps to divert freshwater from the Mae Klong River to the Chao Phraya River, to hold back seawater, as rice growers ignore instructions to stop off-season cultivation.
Mr Chalermchai said on Monday he sent his urgent order to the department because the water level in the Chao Phraya Dam reservoir was very low.
Irrigation department director-general Thongplew Kongjun had reported last week the level was only 13.10 metres above mean sea level.
It had since risen slightly because local administrators were ordered to prevent pumping by local farmers.
"Today it is at 13.19 metres. We must keep a close watch because it is now below the 14-metre level of 2015, which was a year of severe drought," he said.
The seriously low level was despite four main dams discharging 18 million cubic metres of water a day into the Chao Phraya River, he said.
Mr Chalermchai ordered irrigation officials to operate pumps to divert water from the Mae Klong River in the west through Jorakhay Samphan and Tha San-Bang Pla canals to the lower basin of the Chao Phraya in the Central Plains, where salinity could exceed safe levels as seawater pushes inland along the depleted river flow.
He blamed rice growers he said had ignored the government's instruction to suspend off-season rice cropping because of the severe water shortage. He said water was still being pumped into paddy fields along the Chao Phraya River.
Mr Thongplew said the Chao Phraya river basin needed enough freshwater to maintain production of tap water and also supply orchid and fruit plantations.
"Farmers in the Chao Phraya river basin must not grow any off-season rice now. In this dry season, the Agriculture Ministry does not allow off-season cultivation, but farmers have planted rice on as much as 13.9 million rai of fields," he said.
"Off-season rice crops are at risk. The Royal Irrigation Department is reserving the water only for consumption, ecosystems and other crops until the next rainy season," he said.