Second Person Poisoned By Toxic Algae In Lake Hood

Tuesday, 1 April 2025, 9:28 pm
Article: Jonathan Leask - Local Democracy Reporter

A second person has been poisoned by the toxic algae in Lake Hood near Ashburton.

National Public Health Service (NPHS) medical officer of health Dr Cheryl Brunton said the person was jet-skiing last week and fell into the lake several times.

“This happened on the day that a public health warning was issued about a toxic algal bloom (cyanobacteria) in the lake.”

Health New Zealand Te Whatu Ora issued a health warning about the Canterbury lake on March 20.

Toxins released by cyanobacteria can trigger asthma and hayfever symptoms, skin rashes, stomach upsets, and tingling around the mouth, headaches, breathing difficulties and visual problems.

A swimmer was poisoned by the toxic algae prior to the health warning being placed on the lake.

The NPHS was notified of the exposure to toxic algae after the release of a health warning.

This is the third year-in-a-row the lake has had an algae-related health warning in place.

The Ashburton District Council took over management of the lake in June last year, but it was not directly informed of the incidents by Health NZ.

Council infrastructure and open spaces group manager Neil McCann said on Monday the council had not been notified or briefed by Health NZ of the first incident at Lake Hood.

Health NZ released its weekly surveillance report on Monday afternoon showing the second ‘poison by environment’ incident had occurred.

The organisation did contact the council on this occasion.

However, McCann said he was frustrated by a lack of details provided by Health NZ around when and where the incidents occurred.

The council has put a lot of work in over the summer to avoid blooms developing, as well as working on a long-term plan to improve water quality and avoid recurring blooms, he said.

McCann said they have focused their immediate efforts on changing the way water circulates in the lake and canals, by splitting the intake from the Ashburton River and introducing a weed harvester.

Environment Canterbury monitor the water quality in line with national guidelines, including weekly visual inspections.

ECan water and land science manager Dr Elaine Moriarty said if they find the likely presence of an algal bloom, it is reported to Te Mana Ora Community and Public Health and the council immediately.

Algae bloom samples are then sent to an independent laboratory, with the results also shared with council and Te Mana.

“Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips.”

The symptoms may not appear until sometime after contact with affected water, she said.

McCann said the health warning on March 20 was a result of an ECan visual assessment of the lake on that day.

“ECan and Health NZ took immediate action rather than waiting for the results of the water testing to be received”.

Moriarty has defended ECan’s testing regime, which monitors more than 100 recreational sites weekly across Canterbury during summer.

“It’s just not possible for us to be at every site where people swim at all times and conditions can change quickly.

“That’s why alongside our monitoring programme, we also spend a lot of time talking to the community about water quality and the risks around toxic algae.

“Our monitoring season finishes at the end of March, but we will continue to monitor the sites where a health warning is in place until it is safe for the warning to be lifted - and this will include Lake Hood.”

The health warning hasn't closed Lake Hood, but Brunton said people should avoid the lake. Animals, particularly dogs, should not be allowed near the water until the health warning has been lifted.

“People should avoid contact with the water until further notice.

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