Paul Champion is wading slowly around the shallow edges of Lake Ngatu, near Kaitaia in the Far North. Around him, tall spikes of a sedge known to Māori as kuta stab skywards like needles. This lake is a stronghold for kuta. Weavers come here from far and wide to harvest the stems, which vary from the thickness of a drinking straw to the width of a little finger and can reach four metres from their rhizomes in the lake bed to their tips in the air.
Above water, the stems are the deep green of rimu leaves. Below, they can be many colours. Toi Te Rito Maihi, an expert weaver of the north, wrote an evocation to kuta, marvelling at the “yellows and pinks, greens, browns, oranges and purple” of the living fibres and asking, “After harvesting, hung to dry in the darkness, how do your satin-soft strands transmute into gleaming coloured gold? Irresistible!”
Kuta was traditionally woven into soft mats, cloaks and rain capes. It is used much less by today’s weavers, and some of its more specialised uses have been almost forgotten. One of these was associated with grieving: a woman who miscarried or aborted wrapped the foetus in scented moss, raupō fluff and kuta before placing it in a waterway as a gift to the gods.
Champion, who is a principal scientist at the National Institute of Water and Atmospheric Research (NIWA), runs his thumbnail down a kuta stem and folds it open to show me its internal structure. It is hollow, with soft white septa at intervals down the tube, like the nodes of bamboo. Oxygen produced in the green upper parts of the plant is transported down the stems to the base.
Ngatu is a dune lake, a type that usually forms in the hollows of wind-sculpted sand dunes, and becomes stabilised over time. Dune lakes are globally uncommon but abundant in New Zealand. More than a third of the freshwater lakes in the North Island are dune lakes. Most are small and shallow, like this one.
Something on the lake bed catches Champion’s eye, and he reaches down to pluck a nondescript tuft barely showing above the sediment, like the tip of a shaving brush. “How’s your botanical knowledge?” he asks. “You know about monocotyledons and dicotyledons—the two main groups of flowering plants? Well, this is more primitive than them. We call it the tuatara plant.”
The plant’s scientific name reflects its unprepossessing appearance: Trithuria inconspicua. Today, it is found in only a handful of places, including Lake Ngatu and the Kai Iwi lakes north of Dargaville. It has disappeared from most other lakes because it can’t tolerate competition from invasive species. And invasive species have decimated many of New Zealand’s indigenous aquatic ecosystems.
Lake Ngatu is not exempt. This visit by NIWA staff will be the last monitoring survey before an aquatic herbicide is sprayed on the lake to control two species of invasive weed. One of them, hornwort, is so aggressive that a member of the NIWA team calls it the “space invader”: it can fill the water, smothering everything else.
Decades of carelessness and entitlement are the cause of the weed problem. Since Lake Ngatu lies beside one of the few roads that lead to Ninety Mile Beach, car owners used to wash the salt from their vehicles by driving them into the lake. Horse riders rode into the cooling water to refresh their steeds. Just a fragment of an invasive weed—lodged in a mudguard or on a hoof—can lead to a potentially uncontrollable outbreak.
Earthmovers are another vector for weed spread, including machinery used to extract swamp kauri logs from wetlands. So, too, are eel fishers, who move nets and boats from lake to lake, unaware of the pests they may be distributing.
The loss of mauri (life force) from the lakes has been a source of sorrow for iwi with whakapapa connections to them. Kaio Hooper, environmental manager for Ngāi Takoto, which has mana whenua responsibility for Lake Ngatu, tells me his main goal is “bringing back the wairua” of the lake. “The lake’s wairua, our wairua, they are connected,” he says. “Wairua is a feeling you get when you go down to the lake. Like today. There’s pūkeko down there, the water’s looking blue, the kuta’s healthy.”
Hooper holds a bachelor’s degree in environmental science, but says scientific training is only one part of his appreciation of the lake. “The Western side of things helps me understand why these lakes are special. But my spiritual connection comes from the fact that every single day when I was a kid, I would go to the beach, get pipis, then come here and have a wash. This is my turangawaewae—this is where I stand, and this is where my whānau stand.”
While we’re talking at the lake edge, local artist Michael Marsden joins us. He tells me that his father was the noted scholar, tohunga, philosopher and minister Māori Marsden. Hooper says it was Māori Marsden who helped his people understand the connection between identity and kaitiakitanga—the practice of stewardship towards the natural world. In 2015, Ngāi Takoto’s Treaty of Waitangi claim settlement gave the iwi the opportunity to put those principles into practice.
“Settlement made it clear to the councils and other iwi and the community that we should be recognised for our role within our rohe,” Hooper says. “Settlement gave us the identity and the foundation to start enacting the kōrero that Māori [Marsden] taught us around kaitiakitanga and connectedness. Not just about looking after the land but about our relationships with land, with community, with whakapapa.”
For Hooper, lake restoration can never be just ecological; it must be cultural, too. “It’s not just about the lake. We’re rebuilding our people at the same time. Right now, I’m training some of our young people in how to build fences and do riparian planting. It’s all te ao Māori.”
Michael Marsden offers a whakataukī to encapsulate these thoughts: “Ina pōhara te wai, he pōhara te tangata. Ina ora te wai, he ora te tangata.” If the water is poor, then the people are poor. If the water is healthy, then the people are healthy.
Ngāti Kuri, another iwi from the Far North, has been on a similar journey of restoration. Wayne Petera, Ngāti Kuri’s coordinator for wai māori (freshwater), tells me that his people are awakening to the importance of the dune lakes in their rohe, and to their role as kaitiaki.
Petera says the kaitiaki responsibility is an ancestral mantle laid on the shoulders of each generation. “We have no choice in the matter,” he says. “Mana requires that we act.” On the basis that Ngāti Kuri has existed for close to a thousand years, Petera says the iwi has decided it must have a thousand-year vision for itself and its environment, lakes included.
“We recognise that if we are the people we say we are, then we have a deep responsibility to ensure the life and well-being of all of these ecological gems,” he says.
“Yet how many of our people know about these lakes and the stories connected to them? Very few. How do we reformulate our relationship with them? By going to those lakes and sharing the narratives of our tūpuna. Engaging our own people with these taonga. The reclamation of our people is not just through our physical presence but our narratives as well. The narratives are the carrier of the intrinsic message that we belong here.”
There’s an aspect of the narrative Petera describes that I find both challenging and deeply attractive: that dune lakes, as part of the natural world, Tāne’s world, are older brothers and sisters to humans. We are tēina, the younger siblings, while the natural world is tuākana, our older brothers and sisters.
“When you look at our whakapapa and atua, we humans are absolutely tēina,” he says. “Even the fish, through Tangaroa, have greater status than we do. They are tuākana to us. We have a responsibility to our tuākana as they have a reciprocal responsibility to us. But we forgot our part in that relationship. We thought we were tuākana over everything else.”
Now we have our work cut out to repair the damage and restore the flourishing of both ecosystems and cultural connections. Joining iwi in that mahi is the Northland Regional Council (NRC) and its research provider, NIWA, monitoring the ecological health of the dune lakes of the north.
In September, I joined one of their annual “state of the lakes” surveys. It was there that I learned that New Zealand is a global hotspot for dune lakes, and Northland has one of the greatest concentrations in the country. Once you start noticing them on a map, you see blue spots everywhere, like eyes. The eyes of the land.
Environmental historian Jonathan West calls lakes the land’s mirrors, because they hold in their water and sediments a memory of the processes that created and shaped them. Their beds are “nature’s archives”, he writes. They are a lens through which to understand changes to the land and changes to human attitudes to the land.
The survey team based itself at Rarawa Beach, north of Houhora. This is avocado country, where orchards stretch as far as the eye can see. We visited one, owned by Ngāti Kuri, where a 17-metre-deep dam had been dug as a water reservoir and was now providing a site for native plants to regenerate.
NRC biodiversity manager Lisa Forester had spotted the lake during an aerial survey, but this was her first visit. As a cold south wind whipped the water into whitecaps, she struggled into a drysuit and dived under to see what was growing there. Meanwhile, on shore, Champion and other botanists were delighted to find sundews and orchids among a thriving lakeside flora.
NIWA’s survey team has developed a bio-assessment tool called LakeSPI (lake submerged plant indicators) to rate the ecological condition of the lakes. Using plant life as a parameter for assessing lake health is a step forward, one of the dive team tells me. Government regulations now require councils to assess biodiversity in water bodies—not just physical and chemical parameters.
One of the lakes they dived in during the September survey was so turbid, they had to assess plant life by feel. The divers couldn’t see a hand in front of their face. In Lake Ngatu, though, they were pleased to find healthy plant growth down to five metres—a sign of improving water quality. Turbidity is often a sign of a high nutrient load, which is a disaster for New Zealand lakes. Our lakes do best in a low-nutrient, or oligotrophic, state, but that is rarely the condition they find themselves in today. Nutrients such as nitrogen and phosphorus, typically entering waterways through run-off from nearby farmland, turn lakes eutrophic, or rich in nutrients, causing them to bloom with algae, and changing them from clear and healthy to turbid and toxic.
The change can be rapid, and is sometimes irreversible. Freshwater scientists say a lake that has undergone this transformation has “turned over” or “flipped”. Champion has seen it happen time and again. Lake Ōmāpere, Northland’s largest lake, was once the water supply for nearby Kaikohe. In 1985, it flipped. “All of a sudden the water tasted disgusting,” he says. “The surface was choked with the introduced aquarium weed Egeria. The lake flipped from a clear, vegetative state to a turbid, algal state.”
Champion elaborated on the process for me. “In the vegetative state, plants cover the bottom of the lake, stabilising the sediment and taking up nutrients into their tissues. But if the nutrient load exceeds what the plants can absorb, you get algae growing in the upper water column. Turbidity increases, shading the vegetation below.”
Deprived of light, native vegetation is prevented from growing in anything but the shallowest parts of the lake. Native fauna such as freshwater mussels and crayfish are also affected.
If invasive weeds are present, the situation can quickly become dire. A weed such as hornwort can grow to a depth of 10 metres, and many dune lakes are not much deeper than this. Shallow lakes can warm up so dramatically in summer that they “cook” the lake weed within them, causing it to rot. Decaying beds of vegetation remove oxygen from the lake, allowing even more algae to bloom, including toxic blue-green algae, or cyanobacteria. “Once the process starts, it can’t easily be stopped,” says Forester.
She now spends a good deal of her time working on ways to remove problem weeds. One option is to use an underwater herbicide that targets introduced species but not native aquatic plants. This is the approach that was used at Lake Ngatu in early September. Two weeks after the herbicide application, the oxygen weed beds had collapsed.
Another method for controlling invasive plants is to release grass carp into the lakes. These fish have a voracious appetite for freshwater plants, both native and introduced. The idea is that, by reducing the biomass of fast-growing invasive plants, native vegetation will be able to hold on, albeit at low densities. Only sterilised carp are released, so that there is no chance of their population perpetuating itself. Eventually, the fish die of old age or are netted once their work is done—though catching them is easier said than done. On Pouto Peninsula, the northern head of Kaipara Harbour, Colin Taurua and his whānau have watched, bemused, as scientists have made multiple efforts to remove grass carp from one of the lakes on their land. Several wily old carp have eluded capture. I saw one give a mighty splash when I visited the lake with Taurua and other members of Te Uri o Hau hapū.
“That fish is probably 25, 30 kilograms,” said Taurua. Others in the same weight range have been shot by bow hunters sent in to try to eliminate the fish.
At another lake on the property I snorkelled among hundreds of freshwater mussels, watching them bulldoze trails through the soft sediment a few metres from shore. Like marine mussels, these torewai (also known as kākahi) are superb water filterers, removing algae and restoring water clarity. This happened in Lake Ōmāpere. The torewai filtered the lake water and allowed the native vegetation to come away. But where invasive fish or dense introduced weed beds have gained a foothold in a lake, torewai populations typically decline or even disappear.
NIWA’s lake team includes researchers who set fish traps to check for the presence of both native fish and introduced pest species such as koi carp, catfish and perch. One afternoon during the survey, this team brought the exciting news that they had caught eight endemic black mudfish—an at-risk species that is an ecological indicator of water quality—in a wetland near Lake Ngatu.
I had joined them in exploring this swamp. As with many wetlands, the place had seemed unpromising from a distance, but fascinating from the first step I took into its spongy expanse. My feet turned the colour of Coca-Cola as they sank into the tannin-stained water. Water spiders scampered across the meniscus, seeming to walk on air. Several climbed up my legs. I pushed aside tangled tresses of “trip-me-up” vine, Cassytha paniculata, a parasitic plant that was twining around mānuka, drawing nutrients from its host. I savoured the ting, ting, ting call of a fernbird, enticingly close but always just out of sight.
Healthy wetlands like this give heart to biologists: they confirm that Northland’s freshwater bodies remain strongholds of native biodiversity. But agriculture is intensifying in the north, the climate is warming, and invasive species are only ever an accidental introduction away. The region’s dune lakes cannot be considered safe from harm.
How can these taonga be protected? Education is a high priority. At Te Rarawa’s rūnanga office in Kaitaia, I meet Joanne Murray, whose goal is to educate tamariki early about the importance of these lakes. Working alongside NRC and the Ministry for the Environment’s Freshwater Improvement Fund initiative, she runs regular “Get to Know Your Dune Lake” days, where people can learn about everything from the importance of freshwater insects to the traditions of kuta weaving. “We’ve taken rangatahi to harvest kuta and make rain capes and give them away as gifts,” says Murray.
Since education is about connection, not just information, Murray’s group has written waiata about the various lakes, linking them to marae that have a relationship to them.
They teach te mana o te repo, the mana of the wetlands, speaking of the essential role wetlands play as intermediaries between the realms of Tāne (the forests) and Tangaroa (the seas).
In Murray’s work, and in the mahi of advocates of te wai māori across the Far North, I discern the truth of a whakataukī: “Te roto tāpokopoko, he wai whakahuihui, he pukenga ora.” A dune lake is an oasis that gathers and grows life.