A high level of ammonia pollution in Johor's Sayong River, which has disrupted water supply to about 17,000 households in Kulai, also forced Singapore's national water agency PUB to stop treatment operations at its waterworks in Johor yesterday afternoon.
In a statement released last night, PUB said the shutdown at Johor River Waterworks, which it owns and runs, has disrupted its water supply to Singapore and some parts of Johor.
But water supply in Singapore is not affected, the agency added, as it has stepped up local production at the desalination plants and waterworks to meet demand.
It said it is monitoring the raw water quality in Johor River closely and "will resume abstraction and treatment of raw water when water quality is suitable".
Under the 1962 Water Agreement, Singapore can draw up to 250 million gallons of water a day from Johor River, and is obliged to provide Johor with treated water up to 2 per cent of the water imported. Singapore has been supplying more to Johor at its request.
Johor International Trade, Investment and Utility Committee chairman Jimmy Puah Wee Tse said a reservoir at a bio-composite centre next to a palm oil refinery in Sedenak had burst, causing the ammonia-contaminated water to flow into Sayong River, which is one of the creeks that supply raw water to Johor River.
Mr Puah, who is also a Bukit Batu assemblyman, said the incident occurred around 7am on Wednesday, The Star Online reported.
"At around 6.30pm, both the Sayong 1 and Sayong 2 water treatment plants had to be shut down as they could not process the raw water due to high levels of ammonia," he said in a statement yesterday.
He added that the Semanggar, Johor River and Tai Hong water treatment plants had to be shut down.
He said the authorities have taken the necessary action against the palm oil refinery by cancelling its raw-water abstraction licence and serving a compound notice following the incident.
"The Johor government will not compromise over the incident and the Johor Water Regulatory Body has cancelled its water abstraction licence with immediate affect," he said.
Mr Puah said Kulai was the only affected area, adding that the water supply would be restored fully at about 10pm yesterday.
Water contamination has been a constant pain for Johor.
Last month, a water treatment plant in Simpang Renggam in Johor's Kluang district was closed because of ammonia pollution at Benut River, cutting water supply to about 75,000 consumers.
The closure came at a time when close to 6,000 residents in Pasir Gudang were affected by toxic fumes, caused by the illegal dumping of chemical substances into Kim Kim River in the industrial town.
The incident forced the closure of 111 schools in the area.
In October 2017, Singapore's water operations at Johor River Waterworks were also stopped temporarily because of ammonia pollution. The incident affected some 60,000 people in the area.
Several months later, the Malaysian authorities traced the source of that pollution to an unidentified poultry farm that produces fertilisers using chicken manure.