8 hours ago
Lake Ōmāpere hoped to be restored to former glory
Lake Ōmāpere in March this year, when an algae bloom turned the water a lurid green.
Photo:
Supplied / NIWA
An ambitious plan to restore the health of Northland's largest lake is set to begin within a year, funding permitting.
Lake Ōmāpere was once known as the food basket of Ngāpuhi for its abundance of aquatic life, but in recent decades it has become increasingly polluted.
It is also afflicted by algal blooms that turn the lake a lurid green and can be fatal to aquatic life.
Various attempts have been made over the years to save the 1200-hectare lake, just north of Kaikohe, but the Lake Ōmāpere Trust believes the current plan is different.
The Ngā Kaitiaki o Te Roto Ōmāpere Restoration Plan has also caught international attention, with the trust invited to make a presentation to the World Lake Conference in Brisbane next month, even before physical work gets underway.
Trustee Marise Stuart said the lake was in a "hyper-eutrophic state", which meant the water was extremely high in nutrients. Those nutrients provided food for microscopic algae which grew rapidly in summer months, causing algal blooms.
The blooms turned the water bright green, and - depending on the organisms involved - could be toxic, killing creatures both in the lake and downstream in the Utakura River.
Lake Ōmāpere was once known as the food basket of Ngāpuhi. These days it's heavily polluted and mostly devoid of life.
Photo:
Supplied / Paul Champion, NIWA
Stuart said the first bloom occurred in 1984.
"Children swimming in the Utakura River became sick. Animals wouldn't drink the water. The shellfish turned bad. It's what you hear about any kind of algal bloom, but it's right here in our backyard, and it's an ongoing issue."
Blooms had occurred regularly since then, including in 2018. Tests showed that bloom was
not toxic
but it still killed a large number of eels, thought to have been caused by a lack of oxygen in the water.
Stuart said the lake's decline had taken place within living memory.
Trustee Ani Martin, aged 93, recalled the abundance of food the lake used to provide; while her daughter Kay Martin, also a trustee, remembered diving into the lake as a child and seeing tuna (eels) weaving in and out of a thick bed of aquatic plants.
Some of the older farmers living around the lake could recall putting their hands into the water and pulling out handfuls of freshwater mussels.
Neither the plants nor the mussels survived in the heavily polluted lake today, which had serious knock-on effects.
The plants released oxygen while the mussels were efficient filter-feeders that used to keep the water clean.
"So that whole biodiversity that was once there is no longer," Stuart said.
Utakura Valley landowners Neville and Linda Lewis during an algal bloom in 2018, which turned Lake Ōmāpere's outflow bright green and killed large numbers of eels.
Photo:
Peter de Graaf
The lake's problems began with the removal of the surrounding forest in the 1800s, and had been exacerbated by at least three attempts to lower the lake level, starting with the use of dynamite at the lake's exit in 1905.
According to NIWA, the lake was now just 2.6m deep at its deepest point, dropping as low as 1.5m in summer.
Previous attempts to clean up Lake Ōmāpere had focused on riparian planting to prevent sediment and pollutants entering the lake.
A 2012 plan chalked up some wins, but the farm plans were "not as pragmatic as they could have been" and many were not implemented.
The key difference in the latest plan was its focus on sediment already in the lake, deposited there over many decades.
Stuart, who has a Master of Science degree from Harvard University, said years of research had shown that unless that layer of nutrient-rich sediment was dealt with, all other interventions would be futile. Therefore the plan would involve "targeted sediment removal" from the lake bed.
The dredging would be carried out in combination with building sediment traps, more riparian planting around the lake edge, and wetland restoration.
NIWA had also been trialling the use of floating rafts of freshwater mussels, which could help clean up the water.
Another difference with previous plans was the "really strong relationships" built up with surrounding farmers, Stuart said.
"They want to see the lake improve as well. Some of them were there in the days when the water was clean, so they want it to be restored."
There were no plans at this point to raise the lake level, but sediment removal would have the effect of increasing the volume of water it contained, she said.
Much fundraising was required but the trust was hopeful of starting work within a year.
The project was included in the government's fast-track bill, which could expedite the work - though extensive consultation would still be undertaken.
The lake's relatively simple ownership could also streamline the project, Stuart said. Lake Ōmāpere was one of only two lakes in New Zealand where the lake bed and the water were fully owned by iwi. The other was Lake Horowhenua.
A dead eel in Lake Ōmāpere's outflow during the 2018 algal bloom.
Photo:
Peter de Graaf
Stuart said being selected for the 21-25 July World Lake Conference was "massive" for "a humble little lake trust".
"Experts in lake restoration and water quality from all around the world will be at that conference, so it's a really great opportunity to share our story and have some discussion backwards and forwards. It's an affirmation of the hard work and the robust discussions we've had to get where we are."
The Ngā Kaitiaki o Te Roto Ōmāpere Restoration Plan was supported by experts from NIWA and DOC, as well as 2022 Kiwibank New Zealand Senior of the Year Rereata Makiha and internationally acclaimed lake restoration expert Professor David Hamilton.
Far North Mayor Moko Tepania said he was excited about the plan's inclusion of green infrastructure, flood resilience and water resilience.
Far North Mayor Moko Tepania.
Photo:
Layla Bailey-McDowell / RNZ
Water quality problems were starkly evident in
the 2020 drought
when attempts by the Far North District Council to use the lake as an emergency water source for Kaikohe failed due to concerns over algal blooms, he said.
NIWA chief scientist Dr Erica Williams said the institute was supporting the trust's environmental and water quality goals, and working alongside DOC to bring back species such as the endangered aquatic plant Isoetes kirkii.
Hamilton said for too long researchers' philosophy had been "we are the scientists, we know what is best for you".
"This approach fails to recognise and engage with community, iwi and policy makers, particularly Indigenous knowledge holders. Hearing about the Lake Ōmāpere restoration plan will provide the global audience with an opportunity to understand a different, Global South perspective."
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