The Singapore River surprised passers-by on the morning of Monday, October 2, by turning bright green. This change in colour has been attributed to algal overgrowth.
Workers near the river have said that they have been noticing a green tinge and pungent smell from the river for the past two days. "I was quite shocked. I was wondering if it was because the water was polluted," Tina Teng, a service staff member at a seafood restaurant on Boat Quay, told The Straits Times.
The phenomenon of algal bloom has been scientifically termed 'eutrophication,' defined by the OECD (Organization for Economic Cooperation and Development) as "an enrichment of water by nutrient salts that causes structural changes to the ecosystem such as: increased production of algae and aquatic plants, depletion of fish species, general deterioration of water quality and other effects that reduce and preclude use."
Some people have reportedly seen such a phenomenon before, like Asha Azizan, a ticket sales agent, who said: "I usually notice it after heavy rain. I don't think much of it because I figured it is probably a natural thing."
Singapore's National Water Agency PUB has confirmed that the green colour of the water was due to an algal bloom. It added that drinking water in Singapore undergoes proper treatment to remove algae before it reaches homes. Algae, a microscopic organism that grows in water, affects the oxygen content of the water body.
PUB organised quick cleaning operations and the water turned normal by the afternoon of the same day.
Experts have stated that heavy rain, followed by bright sunlight, is the perfect weather for rapid algal growth. The algae live for about seven days before using up all the nutrients in the water body and disappearing.
Extreme algal bloom has been known to kill aquatic creatures by suffocating them and jamming up their gills. Fish farmers have lost millions of dollars over the years due to algal blooms.
Several other water bodies in Singapore have been turned green due to algal growth, like the Marina Bay waters and the Kranji Reservoir, in 2016.
Other parts of the world have also witnessed excessive algal bloom several times. Lake Erie, of North America, has been affected by a potentially harmful algal bloom. Above 800 square miles of Lake Erie's western basin is now bright green.
Ohio also suffered the same fate in September 2017 when the shoreline near North Toledo was overflowing with algal growth, bringing gasping fishes to the shore.
In 2016 too, 400 miles of Australia's River Murray had turned blue-green, disrupting people's water supply during drought conditions.
People around the world have been advised to avoid water with a greenish shade, including activities such as fishing, swimming, diving, etc. People suffering from respiratory diseases, such as asthma, are also advised to stay away from such water bodies.