How to fix Te Waihora/Lake Ellesmere
It’s one of New Zealand’s most important wetland habitats, and it’s also one of our most polluted lakes. Restoring it to its former abundance of birds and fish will take generations, but it’s possible.
For one day in February, volunteers gather at Te Waihora early in the morning to count birds. Armed with binoculars, they survey mudflats and saltmarshes along 58 kilometres of shore, recording every bird they spot. Waterfowl, waders, Arctic migrants, shags, herons, gulls and terns—the volunteers have counted an average of 49,000 birds every year since 2013.
Canada geese and mallards are plentiful, of course, but of the more than 160 bird species found at the lake, most are either migrating or native birds, including critically endangered species: kōtuku/white heron, kakī/black stilt, tarāpuka/black-billed gull and matuku/Australasian bittern.
During a late-afternoon walk along the mouth of the Waikirikiri/Selwyn River a few weeks before the 2021 bird survey, I counted 40 birds within a few minutes, including a busy kāruhiruhi/pied shag rookery and five kōtuku ngutupapa/royal spoonbills.
Back in the 1980s, one-day bird counts returned even higher numbers—92,000 birds, almost twice that of recent surveys. Conservationists argued Te Waihora should be recognised as a wetland of international importance under the Ramsar Convention. It never was designated as such, but its avian and fish diversity (with 45 fish species found in the lake and streams) puts it at the top of the list of New Zealand’s most important wetland habitats.
Te Waihora is also well known as one of New Zealand’s most polluted lakes, with some of the country’s highest concentrations of sediment, nitrogen and phosphorus. The lake collects everything that comes off the intensively farmed land in its catchment. This contamination can poison or smother aquatic plants and creatures, while the super-enrichment of nutrients such as nitrogen and phosphorous triggers algal blooms, including occasionally toxic ones.
During my walk, on one of the hottest days in January, the lower Waikirikiri ran dark green with algae near the last few Selwyn Huts, and the lake was a muddy grey, so stirred up with sediment I couldn’t see the foot I’d stuck in to test the squelching lake bed.
In 2005, Environment Court judge Jeff Smith expressed shock at the state of Te Waihora. “The lake water is in a serious ecological condition,” he said. It sounded as though the lake was essentially dead. But for Liz Brown, the co-chair of a shared-governance group that oversees a long-term restoration programme, Te Waihora remains a living, and life-giving, taonga.
She can remember rowing a boat with her father at Fisherman’s Point across water writhing black and slippery with tuna/eels impatient to head out to sea on migration. She knows there was once a time when whitebait was so plentiful that people used it to fertilise their gardens. At her marae, Ngāti Moki at Taumutu, the kōwhaiwhai patterns in the dining room feature tuna, pātiki/flounder and aua/yellow-eyed mullet—all of which have sustained people for centuries.
The group aims to restore the lake’s ecosystems by cleaning up its catchment. It began with Ngāi Tahu and Environment Canterbury, but now also includes the Selwyn District Council, Christchurch City Council and the Department of Conservation.
“There’s still a lot of bird and fish life here,” says Brown. “But it’s under stress through water pollution.
I view Waihora as a sink at the end of all the drains—it’s the bowl that catches everything. You can’t just restore
the lake; you have to look at the whole catchment.”
Te Waihora is New Zealand’s largest brackish, coastal lagoon, with 20,000 hectares of murky, shallow water. Technically, it’s neither a lagoon nor a lake, but a body of water occasionally opened to the sea by bulldozers cutting a channel at the southern end of Kaitorete Spit. It then closes again as southerlies refill the gap with shingle driven up from the Rakaia.
Today’s lake is less than half of its original size. Waihora is te reo for “spreading waters”, and before the arrival of European settlers, the lake regularly flooded to more than four metres above sea level, sometimes as far inland as Lincoln. The wealth of traditional food-gathering sites was such that it was recorded in a whakataukī: Ko ngā hau ki ētahi wāhi, ko ngā kai ki Orariki. No matter which way the wind blows, you will always eat at the pā of Orariki.
Ngāi Tahu lost these riches in what is known as Kemp’s Deed. Henry Tacy Kemp, acting on behalf of the Crown, bought eight million hectares of land for £2,000 in 1848. The deed’s terms specified that mahinga kai/food-gathering reserves would be set aside for the “present and future wants” of the iwi, but the Crown chose to interpret the term as areas already under cultivation, or places with fixed eel weirs.
Once settlers arrived, they set about digging drains and surveying paper roads, criss-crossing the drying wetlands. Between the 1860s and the early 1900s, Ngāi Tahu leaders repeatedly petitioned the provincial government to stop the drainage of Te Waihora and the destruction of food resources, to no avail. In 1912, legislation to protect Māori fishing rights in the lake failed narrowly.
It took until 1998 for Ngāi Tahu to regain ownership of the lake bed as part of the iwi’s Treaty of Waitangi claim settlement. Now, Brown expects it will take a generation or two to change things for the better.
What we know
Four main contaminants are behind water-quality issues at Te Waihora: nitrogen, phosphorus, sediment and faecal microbes.
Nitrogen enters the lake from surrounding farms, especially those high in the catchment. About 95 per cent of the total catchment’s nitrogen load has washed off agricultural land, with the highest losses from farms on lighter, stony soils in the upper catchment, rather than the heavier soils closer to the lake. Not all of the nitrogen lost flows into the lake—an estimated 3200 tonnes reach it each year. Because nitrogen travels slowly through the aquifer, its full impact can be delayed by decades. Even with no further intensification of farmland, a significant increase in nitrogen loads is already on its way through the groundwater system.
Phosphorus and sediment contamination continues as the result of past deforestation. Increased sedimentation began when drainage channels were cut across the land and the lake was opened to the sea more frequently. Because phosphorus attaches to soil particles, each storm brings more, running off the land into drains, streams and rivers.
The loss of aquatic plants destroyed the lake’s own filtration system. Te Waihora may have never been crystal clear, but it once held vast beds of submerged aquatic plants that helped to keep it clean enough to see the lake bed. These plants would have kept sediment in place, absorbed excess nutrients, and provided habitat and food for fish and nesting sites for birds. In 1968, the storm that sank the inter-island ferry Wahine ripped the beds out, and they never recovered. A small black mud snail, likely an important food source for eels and trout, died out with the plants. Murky water has been the norm ever since.
The trophic level indicator (see graphic below), a measure of water clarity, chlorophyll content, total phosphorus and total nitrogen, provides a good indication of a lake’s health. Te Waihora scores well above 6, which makes it hypertrophic, or super-enriched. (For comparison, Lake Coleridge is usually below 2.) The best estimate for Te Waihora’s pre-European level is somewhere between 4 and 5.
Demand for irrigation chokes the lake.
The Waikirikiri is the only river flowing into Te Waihora that has its source in the foothills and is partially fed by rain. All other streams start with springs bubbling up from the aquifer. With hundreds of resource consents taking an increasing volume of groundwater to irrigate an ever-growing area of drained land, lowland streams sometimes run dry. Whole sections of the Waikirikiri disappear underground. A new irrigation scheme, Central Plains Water, addresses the over-allocation of groundwater by bringing in water from the Rakaia. But it has also been granted resource consent to irrigate an additional 30,000 hectares of previously dry land in the catchment, which will increase nitrogen flows into Te Waihora.
How we fix it
When I lived in Christchurch during the mid-1990s, Te Waihora was a place to drive past without stopping on the way to the Banks Peninsula. But since Ngāi Tahu’s settlement, the iwi, and in particular the rūnanga at Taumutu, have worked to change that perception.
The result is the long-term restoration programme Whakaora Te Waihora, the first joint land management plan between iwi and the Crown in New Zealand.
Reduce the concentration of nitrogen flowing into the lake.
Under Environment Canterbury’s Selwyn Te Waihora Water Plan, dairy farmers with annual nitrogen losses above 15 kilograms per hectare now have to show a 30 per cent reduction before they can renew their farming consents in 2022. This won’t lower the nitrogen load in the lake in the short term, as the Central Plains Water scheme adds more than the reductions on existing farms save. But river flows should improve as the scheme reduces the water take from the aquifer, and the council’s water plan prohibits new irrigation consents.
Recreate small areas of wetland.
Even the best control of nutrient and water flows won’t be enough, according to Environment Canterbury’s director of science, Tim Davie. The real difference will come only once wetlands are restored. “What you really want to do is improve farming practices, decrease the nitrogen and put in wetlands, and do it all in a combined way,” he says. “Wetlands are great for all sorts of reasons, not just to soak up nitrogen.”
A study commissioned to assess the potential of constructed wetlands to strip nitrogen from the water suggests that less than one per cent of the catchment would need to be converted to cut 40 per cent of the total nitrogen load. That’s about 2000 hectares.
One such wetland is now in place at the Ahuriri Lagoon, taking water from the Huritini/Halswell River on a meandering detour, past more than 80,000 newly planted raupō and rushes, before returning it to the river on its way to Te Waihora. The lagoon was once a significant mahinga kai site for Ngāi Tahu, but had been drained completely and used for dairying. Now, the cows are gone and the reconstructed wetland acts as a proof-of-concept in an attempt to convince other landowners to do the same. Pied stilts have already moved in.
Other restoration projects are under way all around the lake shore and in the lake itself.
Replace invasive plants along the edges of waterways with wetland forests.
At Taumutu, one of the earliest settlements in the region, locals have replanted the riparian margins along Waikekewai Creek between the Ngāti Moki marae and the urupā at the old pā of Orariki, bringing the landscape closer to what it once was. Willows are being removed and thousands of seedlings have been planted to bring back wetland forests at the Yarrs Flat wildlife management reserve. Along the Ararira/Lll River, work is under way to stop the mechanical clearing of drainage channels and to replant their margins in the hope of turning them into a network of living streams.
Experiment with engineering solutions to avoid erosion.
In Te Waihora itself, trials are testing floating wetlands and wave barriers to see if they can prevent the shore eroding and buffer the wind, which can sometimes whip all of the lake’s shallow water to one side. (So far, attempts to restore the aquatic plant beds have largely failed.)
Even the lake-opening regime has changed from releasing the water mostly when levels threatened flooding of neighbouring farmland. It now takes other issues into account, such as fish migration and bird nesting.
Selwyn is the fastest-growing district in New Zealand, and while this brings more pressure to increase production from the land, it may also prompt a shift to new ways of farming and living within the natural conditions of the landscape.
The Whakaora Te Waihora restoration initiative lays out a vision that stretches across generations, and within such timeframes, climate change may also nudge land use in a very different direction.
Liz Brown says she’s not giving up on the dream that Te Waihora will eventually live up to its original name: te kete ika o Rākaihautū, the fish basket of Rākaihautū.