Residents queasy over fishy pong
HUNDREDS of dead fish were found floating along and washed up on the banks of a river in Bishan-Ang Mo Kio Park on Tuesday, alarming residents and causing a stench.
National water agency PUB said in a statement on its Facebook page yesterday that it received a report about several dead fish on the upstream section of the 3km-long river - between Marymount Road and Bishan Road - on Tuesday morning.
It was later found that about 400 tilapia and mayan cichlids - freshwater fishes common in the aquarium trade - had died.
Other fish and animal life in the river, including terrapins, were unaffected.
Contractors were sent down to remove the dead fish. The clean-up was completed at 3pm yesterday.
PUB staff collected water samples for testing and found nothing amiss - there was no contamination and water quality was not affected.
"However, due to the hot and dry weather, there are lower levels of dissolved oxygen in the water, which could have led to the death of the fish," said the PUB statement.
The agency also assured the public that the water supplied to households is treated at the waterworks "to World Health Organisation drinking-water quality guidelines".
Dr Tan Heok Hui, a fish expert at the National University of Singapore, told The Straits Times that dry weather could have lowered the river's water level and increased algal growth. This could have led to low oxygen levels as algae competed with fish for it.
The dead fish "could have a low tolerance to oxygen deprivation" compared with the other species, he said, adding that terrapins breathe air like humans do and, thus, would remain unaffected.
Residents interviewed by The Straits Times said that they spotted the dead fish on Tuesday.
Several long-time residents said this was the first time they had seen mass fish deaths in Bishan-Ang Mo Kio Park.
Such incidents are more common in seawater.
In 2009, a plankton bloom killed 400,000 fish off Pasir Ris. Last July, thousands were killed at farms off Lim Chu Kang due to low oxygen levels.