A Queenstown resident’s crying foul over the state of picturesque Lake Hayes this summer, with parts of the lake inundated with “primeval … distinctive green slime”.
But Otago Regional Council on Wednesday removed the ‘no swimming’ signs from around the lake after results from a composite sample taken on Monday showed the presence of the potentially toxic blue-green algae, a form of cyanobacteria, was at a “relatively low biovolume”.
Queenstowner Jeff Williams says it’s the second time in two weeks the “dreadful” algae’s been floating in the water.
The most recent outbreak, on Sunday, was “even more horrific” than the first bloom, around February 15.
“If people saw what it was like, they’d be gobsmacked.
“This is pretty nasty.
“It’s like some toxic factory dumped some green slime in to the water … it’s bizarre.”
ORC environmental regional scientist Rachel Ozanne says it’s sampling water for E.coli at popular sites weekly, and does “visual inspections” for potentially toxic algae at the same time, but also relies on the public to notify them if they spot anything off.
The council then takes weekly samples to test for algae till it subsides.
While the lab results from Monday’s testing at Lake Hayes, received on Wednesday, show it’s safe for swimming again, Ozanne says people still need to be careful around the northern end of the lake because the algae can bloom again overnight.
“Look out for green discolouration in the water, and don’t swim if you have doubts,” she says.
Cyanobacteria first bloomed in Lake Hayes in 2018 – that was the first time since 1981 the algae had been spotted in the lake.
At that time Ozanne called it “highly unusual”, and said its occurrence was attributed to the long, hot, dry summer.
The recurrence this year’s likely due to a combination of factors, including available nutrients in the water, warmer temperatures, more sunlight and last month’s heavy rainfall.
Exposure to the blue-green algae can cause skin rashes, nausea, tummy upset, and tingling and numbness around the mouth or tips of fingers.
It’s also not safe for dogs – if puppies show signs of weakness, collapse, vomiting, diarrhoea, respiratory or neurological problems, contact a vet immediately.
Symptoms can occur within 30 minutes of exposure and up to 24 hours after.