About 180 Lake Hood residents gathered at the Lake House restaurant on Monday night to hear how the Lake Hood Water Quality Taskforce is battling algal bloom, which has seen a health warning on the lake since January.

Taskforce Chair David West welcomed Mayor Neil Brown, Council chief executive Hamish Riach, councillors, Ecan councillor Ian Mackenzie, and introduced the taskforce and expert advisors who are helping to tackle the cyanobacteria.

Mr Riach said it was great to see groups, organisations, experts, and residents come together to problem-solve the new water quality issue at Lake Hood.

“It is the second time the 22-year-old lake has had a health warning placed on it, but the taskforce has already made good progress since the first algal bloom in May,” he said.

The purchase of a weed harvester, an aerator trial,  commissioning of a NIWA report and extensive research of mitigation options globally were the first steps. The NIWA report would inform the development of a management plan.

“They’re getting the right scientific advice to narrow down a range of options to what will be the best fit for the lake, and its community,” Mr Riach said.

He was also impressed by the range of questions and solutions that residents put forward for the taskforce to consider. “It’s great to see the community being open and honest with their ideas and questions.”

Phycologist and water quality scientist Donna Sutherland joined remotely to help answer questions She specialises in algae-based bioremediation of pollutants in aquatic systems.

Dr Sutherland said that algae need several conditions to thrive, with the one aspect being targeted by the taskforce being the control of nutrients.

She said that having a small amount of weed is helpful in balancing nutrients, and the weed harvester that Council has agreed to purchase will help control growth from this coming spring.

Mr West said the weed is like a lawn, it helps keep the lake floor in control and takes nutrients out of the water, but too much weed would interfere with the nutrient balance.

Residents were told that no more grass carp would be added to the 3000 or so previously introduced to the lake to manage weed levels. As many have outlived their lifespan, a natural reduction in carp would also reduce nutrient recycling in the lake.

The presentation said that cyanobacterial blooms have been increasing in number around the world and are being exacerbated by climate change. New Zealand has not been immune with health warnings on 26 locations in Otago, Southland and Canterbury alone this summer, so the issue was not isolated to Lake Hood.

Environment Canterbury’s regular testing of cyanobacteria shows that levels in the lake are increasing, so Council continues to advise people to take heed of Te Whatu Ora’s health warning and avoid all contact recreation in the lake.

Regular progress updates will be published on the Council website.