Bright green water at Chadwick Lakes is a natural phenomenon and had no significant harm on the marine species there, a leading marine biologist said.

Many were alarmed to see the water at Chadwick Lakes turn bright green, however, expert Alan Deidun noted, the waters there normally turn green towards the end of the rainy season. 

This is mainly due to the high concentration of nutrients in the water.  

“These nutrients most likely leach from the surrounding fields after runoff from heavy rainfall, as a result of intense fertiliser use in local agriculture,” Prof. Deidun said.

The nutrients fuel a bloom of phytoplankton populations in the water, turning it into a rather alarming shade of green. 

The phenomenon, a disturbance known as eutrophication, can result in the depletion of oxygen levels and in blocking out sunlight, necessary for marine life using the light for photosynthesis, Prof. Deidun said.

Most of the species in the water were probably adapted to its occurrence, given the site was a heavily-impacted and disturbed one. The site was also “far from pristine”, he said.

The phenomenon will fizzle out with the onset of the dry season in a few weeks’ time, he added.

Greater promotion of organic farming, a lower reliance on artificial fertilisers and a greater reliance on slow-release natural fertilisers, such as manure, would help mitigate but not eliminate the annual phenomenon, Prof. Deidun said.

An extensive bioengineering programme will be included as part of a rehabilitation programme of Chadwick Lakes. Environmental authorities are looking to eradicate alien species and allow native habitats to thrive.

Ambitious restoration plans for the sensitive valley and watercourse will involve the elimination of several plants, including species of acacia and prickly pear, which have a negative impact on existing habitats.

Phytoplankton turned the water at Chadwick Lakes into a bright shade of green. Photo: Jonathan Borg