PUB and the National Environment Agency (NEA) thank Dr Ong Siew Chey for his letter ("Chemical link to mass fish deaths?"; July 28).
Cypermethrin was not detected in the water samples taken from the Kallang River after the fish death incident.
However, water samples collected from an upstream tributary drain of Kallang River showed presence of sulphide and elevated levels of ammonia, which may have come from used water discharged into public drains. This is the likely cause of the fish death.
We advise the public that used water should not be discharged into the drains but into sewers.
Drains are meant to convey rainwater to our reservoirs or the sea.
PUB and the NEA will continue with checks of the area for sources of pollution, and will not hesitate to take enforcement action against any illegal discharge into public drains and canals.
The public can report any pollution acts by calling NEA's 24-hour call centre on 1800-CALL NEA (1800-2255-632) or PUB's 24-hour call centre on 1800-284-6600.
Director, Catchment and Waterways
Fong Peng Keong
Director, Pollution Control Department
National Environment Agency