If the threat of crocodiles and deadly jellyfish were not enough to keep people out of the ocean in Darwin, a bloom of toxic algae has prompted an official warning to swimmers.
The Northern Territory’s Environmental Protection Authority (NTEPA) said the green blue-green algae floating in the water off the coast of Darwin’s foreshore area was a natural phenomenon, but that it should not be ignored.
Over the weekend, concerned residents contacted the Pollution Control Hotline reporting what appeared to be an extensive oil slick, with a bad smell, in the water off the Nightcliff foreshore.
What is blue-green algae?
- A blue-green algal bloom (sometimes referred to as cyanobacteria) is a common term used to describe an increase in the number of algal cells to a point where they can seriously reduce water quality.
- Blue-green algal blooms can discolour water, form surface scums and slicks, produce unpleasant tastes and odours and create problems for aquatic life and water users.
- Algal blooms vary in colour, from green to blue, red, brown, dark green or black.
- Some algal species have the potential to produce toxins. As a bloom ages or begins to die, concentrations of toxins may increase. Toxins may persist for a number of months before they are degraded by sunlight and microbial activity. Toxins may continue to exist in the crust of dead, dry algae for months.
- Contact with blue-green algae during water based activities can cause skin, eye and respiratory symptoms. Blue-green algae toxins have been identified to occur in some seafood, which can be harmful to people if consumed.
- Slicks of blue-green algae can be so large they are visible from space.
- The algae does not survive for long for various reasons, including damage caused by UV radiation, and soon start to go “on the nose”.
Dr Bill Freeland, head of the NTEPA, said algae blooms were common for this time of year.
“Don’t go paddling, don’t go swimming,” he said.
“Swimming would be a high-risk activity.”
Dr Freeland named the main culprit – an organism called trichodesmium – which is not considered problematic for humans, but which could be accompanied by other, more dangerous bacteria.
“There are other kinds which could be present, which cause skin irritation and do have very toxic properties,” he said.
In September 2013, Australian scientists helped to establish a potential link between blue-green algae and motor neurone disease.
A spokesperson for the EPA said that beaches around Darwin remained open, but that the situation could change if conditions worsened.
Darwin resident Toby Clifford said the multicoloured algae, while in possession of some “psychedelic colours”, was not pleasant for the nose, and he would avoid the water until it cleared.
“I usually take the dog for a walk down there. But we won’t be going in for a while,” he said.
Dr Andrew Negri from the Australian Institute of Marine Science (AIMS) said trichodesmium was commonly mistaken for an oil slick.
“Trichodesmium is omnipresent in the oceans. It does a lot of useful things for the environment,” he said.
Scientifically, Dr Negri said, it was easy to identify.
“Scoop up a quantity in a glass or container… if the contents are shaken and then let stand for several hours, the water at the bottom will turn purple due to pigments dissolving.”
He said that trichodesmium, along with many other naturally occurring organisms, had proved almost impossible to study in a laboratory environment because it was hard to replicate the natural conditions under which it thrived.
The AIMS website noted the most useful observations on trichodesmium “remain those made by Captain Cook over 200 years ago”.
Photo: Environment authorities have warned Top Enders against going into the water after a blue-green algae bloom off Nightcliff beach. (Supplied: Toby Clifford)
View original article at: Blue-green algae bloom prompts swimming warning for NT beachgoers