SINGAPORE – Investigations into the fish die-off and pinkish-purple colour of the Sentosa South Cove waterway earlier this month have found that it was caused by the recent weeks’ heavy and persistent rainfall that altered water conditions.
Water samples tested had low levels of salinity and dissolved oxygen, which may have led to the dead fish sighted on the waterway banks from Jan 6 to Jan 9, said the Sentosa Development Corporation (SDC) and National Environment Agency (NEA) in a joint statement on Sunday (Jan 17).
The algal bloom that changed the colour of the waters was likely triggered by a high nutrient level and organic content in the water, NEA added.
Sentosa Cove residents first noticed a foul, sewage-like smell coming from the waterway on Jan 5. This was followed by the fish kill, and the waters turning shades of plum from Jan 12.
SDC and NEA, together with Sentosa Cove Resort Management (SCRM), studied water samples collected between Jan 6 and Jan 13.
The National University of Singapore’s (NUS) Tropical Marine Science Institute (TMSI), which was tapped by SDC and SCRM, found high amounts of pico-cyanobacteria – a form of algae – in the water samples.
The colour of the bloom depends on the species of the algae and their pigment composition, and the algal bloom could have occurred even before the visible change in the colour of the waters, the SDC-NEA statement said.
In line with what experts told The Straits Times in earlier reports, SDC and NEA said that the dead fish could also be due to the low level of oxygen caused by the cyanobacteria’s respiration or decomposition, or suffocation due to gill clogging. The statement added another possible cause – irritation caused by the algal bloom.
The unpleasant odour of the waters was likely due to decomposing fish, Sunday’s statement added.
In a letter sent to residents on Jan 11 seen by The Straits Times, Knight Frank Property Asset Management on behalf of SCRM said the “largest clean-up and haul of dead fish” had been conducted.
Marine experts identified rabbitfish, moonfish, batfish and leatherjacket fish among the dead fish.
ST has contacted experts and Sentosa residents for comment.
