Record season for Punahau Lake Horowhenua weed harvesting

Horizons Regional Council is celebrating a successful season of lake weed harvesting at Punahau Lake Horowhenua, with a record amount of weed removed from the lake.

The harvesting, which occurs annually, is the result of a partnership between Horizons, lake owners Lake Horowhenua Trust, and Muaūpoko Tribal Authority under the Lake Horowhenua Accord.
Horizons chair Rachel Keedwell says removing the weed via harvesting helps to improve the health of the lake.
“The weed harvesting project, which has been running since trials were completed in 2021, was identified as a key intervention in addressing the internal lake processes which lead to toxic conditions for aquatic life – including elevated pH and ammonia levels, and cyanobacteria blooms.
“These toxic conditions not only make the lake unsuitable for recreational use, but also have negative impacts on fish and other aquatic life in the lake, which can also impact the estuary and coastal environments further downstream.
“Following the successful trials in 2021, the weed harvester has been operating each season, running from December to February. This is because the warmer weather and increased hours of sunlight causes weed growth to take off again,” she says.
Lake Horowhenua Trust deputy chair Dean Wilson says that the collaborative approach to improving water quality in the area has been a positive step.
“Punahau is a taonga for Muaūpoko, and the condition of the lake has a significant impact on the spiritual wellbeing of our people. We remain hopeful that our partnership will one day see our precious taonga restored, and go some way to easing some of the deep mamae caused by its pollution.
“Our ultimate goal is to restore the mauri of the lake so our tamariki and mokopuna can visit and enjoy the area as our ancestors were once able to.”
Muaūpoko Tribal Authority chief executive officer Di Rump says the partnership is one of a variety of strategies between the Trust, Muaūpoko Tribal Authority and the Council.
“This is a continuation of the mahi which commenced under the Lake Horowhenua Accord. Since the formation of the Accord, we have been working towards improving lake health.
“We hope to continue these efforts so one day this place will be a healthy and thriving ecosystem and recreation destination,” she says.
Horizons group manager catchment operations Jon Roygard says there are two main weed species harvested during the process.
“We harvest curly pondweed (Potamogeton crispus) and elodea (Elodea canadensis) from the lake. Harvested weed is then taken to a composting facility, so it’s not wasted.
“During the last harvesting season the team removed 425 tonnes of lake weed from a 79 hectare area of the lake, which is the most ever harvested in one season.
“It’s a commendable effort, and couldn’t have been achieved without our partnership with the Lake Horowhenua Trust and Muaūpoko Tribal Authority. Their continued support and cultural monitoring of the project enables this work to happen each year,” he says.
Further information about interventions to water quality in Punahau Lake Horowhenua and the wider Waiopehu catchment can be found on Horizons website here: