Residents of Sentosa South Cove witnessed a rather strange sight on Tuesday (12 January) afternoon when the waterway turned pinkish-purple while emitting a foul, sewage-like smell.
It appears that the rotten odour began wafting from the waterway on 5 January, and it got stronger over the next few days. However, from Wednesday (6 January) last week to Sunday (10 January), dead fish were seen floating near the banks.
Images of the pink-hued waters and dead fish floating on the surface were shared on Singapore Marine Guide’s Facebook page.
The “largest clean-up and haul of dead fish” happened last Saturday, said Knight Frank Property Asset Management on behalf of Sentosa Cove Resort Management (SCRM), in a letter sent to residents on Monday.
An SCRM spokesman said to The Straits Times (ST) that the dead fish were first discovered in the waterway of South Cove between 6 January and 10 January. On Tuesday, the colour of the waters changed. However, the North Cove waterway has not been affected.
The resort management also revealed that it is working on the investigations with the National Environment Agency (NEA).
Looking at the corpses of the fish, marine experts identified some of them as rabbitfish, moonyfish, batfish and leatherjacket fish.
“As a precautionary measure, SCRM has advised residents to refrain from water sport activities in the waterway. SCRM will continue to monitor the waters,” the spokesman said.
Explaining about the change of colour in the waterway, Dr Sandric Leong, senior research fellow at the National University of Singapore’s Tropical Marine Science Institute told ST that it happened due to a pico-cyanobacteria bloom, which is a form of algae bloom.
A bloom occurs when a large amount of algae or cyanobacteria collects in the water, resulting from high amounts of nutrients such as phosphorus and nitrogen.
Dr Leong also noted that heavy and continuous rain over the last few weeks may have contributed to the bloom.
“The fast-adaptation characteristics of cyanobacteria to sudden changes in environmental conditions, like the recent continuous rainfall, enable cyanobacteria to outcompete other phytoplankton or algae. Due to the rainfall, the light condition was low, and cyanobacteria could grow better in low light levels,” he explained.
The NEA noted that nothing shows that any industrial or marine pollution could have affected the waters in the surrounding area.
When algae bloom happens, it can remove dissolved oxygen from the water, which is harmful to marine life. However, experts asserted that it is not clear if the fish deaths and pink-coloured water are linked, ST reported.
Additionally, the experts also pointed out that water circulating between the waterways and seawater beyond South Cove can help in breaking down the algae and bring in fresher saltwater. This then will increase the oxygen levels in the water.
Some of the common causes that could lead to fish death are lack of oxygen, toxins produced by algae bloom, as well as high concentrations of algae species that can affect the gills of fish, said Associate Professor Federico Lauro from Nanyang Technological University’s Asian School of the Environment.
A resident told Mothership on Wednesday (13 January) that she did not see anything wrong, adding that the waters have also changed to its original colour, but they seems to be slightly “grey” when it used to be green.