Visitors to Bishan-Ang Mo Kio Park have been noticing, since Tuesday, what appears to be an oily substance on the surface of the river water there.
Mr Joshua Sng, 34, who is self-employed, said: "I don't know where it came from but it can't be good for the park's ecosystem."
The river smelled like kerosene, said others The New Paper spoke to. One local resident said he could even smell it from his 11th-storey flat.
Residents said they had seen oily patches in the river before, although they were much smaller.
"The substance used to appear in small patches, but the patches were much wider on Tuesday. I even saw fishes leaping out of the water for air," said a resident who declined to be named.
When TNP returned to the scene yesterday, much of the oil-like substances had dissipated.
Officers from the national water agency PUB were also at the scene to take water samples.
A spokesman said PUB had received a report about the oily sheen around 6pm on Tuesday, adding that it is not likely to be kerosene.
Dispersants had been applied to disperse the oil. Rain yesterday afternoon also diluted any remaining oil.
On-site checks showed no abnormality in the water quality and fish behaviour, the PUB spokesman said.
PUB also said that the water, which flows into the Marina Reservoir, would not have its quality compromised because of the substance.
"PUB would like to assure the public that it has a comprehensive system to monitor the quality of the raw water in our reservoirs, and the raw water is treated at the waterworks to World Health Organisation drinking water quality guidelines before it is supplied to households."
This article was first published on Dec 18, 2014.
Get The New Paper for more stories.