Source: Radio New Zealand
Rising nitrate levels in drinking water have dominated Canterbury’s water quality debate, but anglers, conservationists and scientists are also worried about the environmental effects, with many rivers and streams testing well above the national bottom line. In the third of a three-part series, Keiller MacDuff reports on the people fighting for the health of the region’s waterways, which they say are being degraded by a toxic combination of water being taken for irrigation and nitrates in the service of intensive dairying.
Retired Canterbury fish veterinarian Peter Trolove has been a keen angler since he was a boy but these days he is more likely to be dipping a sample jar into the water than a fishing line.
The Federation of Freshwater Anglers past president regularly traces a loop from his Rangitata Huts home to the Halswell River, stopping to take samples from more than a dozen rivers, streams and drains to record nitrate levels.
A walk along the banks of the Selwyn River ahead of his routine testing reveals the depressing reality of a once thriving river.
Peter Trolove has been taking nitrate readings from rivers and streams around Canterbury for six years. RNZ / Nate McKinnon
“I probably walked about two or three kilometres upstream, there are some good pools and the sun is such that you can see under the banks, and I didn’t see a fish,” he said.
“This river was considered one of the best trout fishing rivers in the Dominion prior World War Two. Up until the 1970s, about 40,000 trout would go through the traps and now they’d be on the numbers of one hand.”
Trolove trained as a veterinarian then worked for the dairy industry before heading overseas to retrain as a specialist fish vet, earning a masters in aquatic veterinary pathology.
He blames intensive dairy farming and a lack of central and local government leadership for declining Canterbury fish stocks.
“I was a dairy vet, I come off a farm, if there was a solution, I’d tell you. The hard truth of it is, you’ve got to farm less intensively,” he said.
A moss-covered sign at the Chamberlain’s Ford entrance to the Selwyn River [https://www.rnz.co.nz/news/national/346261/toxic-algae-warning-for-swimmers-and-pets
warns of high levels of toxic algal bloom], a neurotoxin that can be harmful to people and lethal for dogs.
The sign is barely visible, hidden by foliage as tall as the sign itself, and it is hard to know when or if the arrow indicating the risk level was last adjusted.
For Trolove, it serves as a neat metaphor for what he believes is buck-passing and a lack of care about the environment.
He believes decision-makers see anglers as an obstacle to growing the economy, yet fishing is “quite a significant economy in it’s own right”, along with tourism income from overseas anglers and the risk to “brand New Zealand”.
A moss-covered sign at Chamberlain’s Ford campground warns of high levels of toxic algal bloom, a neurotoxin that can be harmful to people and lethal for dogs. Algal blooms occur naturally but are fuelled by fertiliser run off. RNZ / Nate McKinnon
More than a million cows
Since 1990, Canterbury’s dairy herd has increased by about 1000 percent, to well over a million cows.
Between 2002 and 2019, nitrogen fertiliser use in Canterbury increased 326 percent, while the area being irrigated increased by 99 percent over the same period.
According to StatsNZ, Canterbury had the largest amount of irrigated agricultural land (480,000 hectares) in the country in 2022 and accounted for 70 percent of the country’s total dairy farming irrigation.
The regional council said it did not keep information on the area under irrigation.
An Earth Sciences New Zealand-led study published in November confirmed that Canterbury has the highest percentage of elevated groundwater nitrates in the country, following testing of 3800 rural drinking water samples from private wells between 2022 and 2024.
Researchers used dual nitrate isotope testing, known as a “chemical fingerprint”, to identify cow urine as a primary cause.
The nitrate-nitrogen limit in drinking water is 11.3 milligrams per litre (mg/L) but the standard to protect aquatic ecosystem health is far lower.
The bottom line for nitrate toxicity in the national policy statement for freshwater management, which the government has signalled it will replace, is 2.4 mg/L.
While 2.4mg/L was a steep drop from the previous limit of 6.9mg/L, many believe the figure is too high to protect the health of rivers.
The latest regional council testing of nine Selwyn rivers, streams or drains found all were well above the national bottom line.
Scientists and environmental groups argue other effects of nitrate, including runaway weed and algal growth fed by agricultural fertiliser run-off, cause big drops in oxygen levels in rivers and lakes, suffocating fish at far lower levels.
‘They can’t die twice’
Victoria University freshwater ecologist Dr Mike Joy said the 2.4mg/L freshwater nitrate limit was based on a “false flag” and did little to protect ecosystem health and biodiversity in Canterbury waterways.
“2.4mg/L is about nitrate toxicity, which is a non-existent problem, it’s way less than that where you get algal blooms and hypoxia from lack of oxygen, which is what gets rid of the fish,” he said.
“I would go on record as saying the only fish that ever died of nitrate toxicity in New Zealand were the ones in the fish tank when they were coming up with that number. They’re already dead at 1mg/L because at that level you get algal blooms and the algae takes up the oxygen.”
Joy said there was no single reason for declining fish stocks but intensive agriculture was the common thread.
“Less water, more nitrates, climate change, stop-banking. It’s never one thing, it’s a combination of things,” he said.
Victoria University freshwater ecologist Dr Mike Joy says intensive dairying on the Canterbury Plains has created a feedback loop of water extraction and nitrate pollution. RNZ / Samuel Rillstone
Water takes fuelling increased nitrate levels
Joy described a “feedback loop” of large scale water extraction for irrigation transforming the Canterbury plains into one of the country’s dairy hubs.
“The extraction is what you need to have that intensity of cattle. You couldn’t have that many cows without the irrigation, that means you have way more cows per hectare because you’ve got the water to be able to grow the grass, so then you’ve got more cows, more urine, more nitrate pollution,” he said.
“Less water in the river means higher concentration of the nutrients but before we had irrigation we didn’t have cows and so we didn’t have a problem.”
A February regional council report noted serious limitations on the council’s water data, including around 20 percent of water-take points not providing data, an improvement on the 40 percent that were not providing infomation when the report was last prepared a decade ago.
In 2020-2021, 3636 million cubic metres of water was taken from Canterbury’s surface and groundwater sources, the vast majority for irrigation.
In September regional councillors voted nine to seven in favour of declaring a nitrate emergency, although some branded the move a political stunt, virtue signalling and an attack on Canterbury farmers.
Joy said he held little hope the declaration alone would improve the region’s water quality.
“Big deal, call an emergency, but you’ve got to do something about it before it means anything,” he said.
A fading way of life
Salmon Anglers Association president Paul Hodgson said he had witnessed the decimation of salmon and other fisheries.
“I’ve been out to the Selwyn in the last few years and instead of having a diverse aquatic life and bugs and beetles and all sorts of things, the only thing of any great quantity that’s in the river is snails, and that’s usually the last thing to go,” he said.
New Zealand Salmon Anglers Association president Paul Hodgson is angry years of warnings have fallen on deaf ears. RNZ
Anglers spend hundreds of hours, year after year on the water, and saw changes first-hand, Hodgson said.
“When I used to go fishing, you’d look at the side of the river and you’d see this black line of silveries coming in. There had to be millions of them coming in. The silveries – known by a number of different names, including Stockell’s smelt, stocko and others – they underpin the food web. Once they disappear, they’ve gone and the whole network around the river disappears,” he said.
The association has embarked on an oral history project to record memories of what Hodgson feared was a fading way of life, affecting both anglers and the social fabric around the river.
“The river mouths often have baches or cribs and there’d be anglers in every single one of them, now it’s more like they’ve become retirement homes. The anglers have sold up and shifted out because it’s just simply not worth going there anymore. It’s almost like there’s been a death in the family,” he said.
Hodgson said his father, also a keen angler, warned of the decline decades ago.
“People of his generation were concerned enough to write letters to ECan and to chase up Fish and Game and to chase up the Department of Conservation, we’d go, ‘hey look guys, are you seeing this?’ And all the things that we talked about have now happened or are happening,” he said.
The situation had reached a tipping point, Hodgson said.
“If you can’t go to the river and eat the fish in the river, if you can’t go to the river and swim in it, if you can’t go to the river and drink the water, where are we at? Where do we go from here? Because that’s where we’re at today,” he said.
’20 years too late’ to be gathering information
Canterbury Regional Council is responsible for managing land and water use, setting pollution limits, issuing resource consents, managing water takes and designating drinking water protection zones.
A spokesperson said some surface water and groundwater zones were overallocated and had been so when the current regional plan became operative in 2015.
“This plan set allocation limits, which in many catchments had already been exceeded,” they said.
Asked to clarify which, or how many water zones were overallocated, the council did not respond before deadline.
Its latest annual groundwater survey showed nitrate increasing in 62 percent of the 300 test wells.
More than 10 percent of wells tested had nitrates above the drinking water limit, including 18 of the 56 test wells (31 percent) in the Ashburton zone.
Since the start of 2025, when a temporary [https://www.rnz.co.nz/news/country/580278/thirty-two-more-dairy-farms-for-canterbury-some-grain-growers-go-for-milk
restriction on intensive dairy conversions] ended, the council has issued discharge consents allowing for a potential increase of up to 25,800 dairy cattle.
Some Canterbury dairy farmers are striving to limit nitrate leaching by planting special crops and experimenting with new winter grazing systems.
Chair Deon Swiggs voted against declaring a nitrate emergency when the previous council narrowly passed a motion brought by outgoing councillor Vicki Southworth.
He told RNZ he stood by that decision but hoped the declaration would raise awareness about nitrate.
“Once people have a bit more understanding of what it is we can work with the industry to start addressing some of the problems where there are hotspots and where there are issues,” he said.
“The science people are working with other scientists around the region as well to start standing up the science, start standing up the industry response so that everybody can get on the same page. The last thing we want is people to not believe there’s is an issue when there potentially is an issue.”
Swiggs said the council had no choice but to follow rules set at a national level and cautioned against singling out dairy farming.
“Nitrate comes from all sorts of different sources. If you’re trying to pin nitrate just on cows, nitrate is because people are putting nitrogen onto the soil. All land use activities, including farming for food production, uses nitrate,” he said.
Asked about nitrate isotope testing confirming the dairy industry as a primary source, Swiggs said, “We have a lot of cows in Canterbury”.
Deputy chair Iaean Cranwell, who voted in favour of the emergency declaration, said issue was “very complex”.
“We know there’s an issue in Canterbury and I think everyone agrees there’s an issue across all communities,” he said.
“Even though there was work happening and there were conversations, it wasn’t out in the open. I think all that [the emergency declaration] has done is actually saying we have an issue and what are we going to do about it?” he said.
Regional council deputy chair Iaean Cranwell says the council is hamstrung by central government mandates. RNZ / Nate McKinnon
Cranwell said the council could consider mandating lower dairy stocking rates – Canterbury has the highest in the country, according to Dairy NZ – but it would need to go through a planning process “hamstrung” by the upheaval of freshwater and resource management laws.
The government’s move in July to halt all council planning work until Resource Management Act reforms were complete had further complicated its response, he said.
“If the regulation allowed that, I’m sure that’s one thing you could look at, but at this current time we cannot look at our planning regime,” Cranwell said.
Otago University research fellow Marnie Prickett criticised the council’s approach.
“That’s just not good enough. It’s not leadership, it’s treading water and it’s not acting in the interests of their people who are relying on them to protect their drinking water,” she said.
Along with fellow academics Dr Tim Chambers and Professor Simon Hales, Prickett presented to the council in March, calling for [https://www.rnz.co.nz/news/national/544734/academics-call-for-urgent-action-on-nitrate-pollution
urgent action on the “water pollution crisis”].
The trio advised the council to conduct an independent analysis of why nitrate levels keep rising, look at gaps in the council’s data collection and request the auditor-general conduct a conflict of interest review, all things that could be done regardless of central government reforms, she said.
It was 20 years too late to be talking about gathering information, raising awareness or standing up the science, Prickett said.
“We’re beyond the point where we have to identify what the problem is. I think we know what the problem is.”
University of Otago research fellow Marnie Prickett says the regional council’s response to the water pollution crisis is not good enough. RNZ / Nate McKinnon
Grief for a lost river
As he sets off on another round of water sampling, Trolove is motivated not only by his love of the rivers and streams but the loss of possibilities for his children and their children.
“It pains me that the next generation won’t have what I had,” he said.
The way decisions were made that has left some without safe drinking water and whittled away fishing spots to remote high country rivers made his blood boil.
“Where is the equity for the ratepayer in Selwyn who looks like paying $400 million for Rolleston to go and develop source water near the Waimak (Waimakariri) to pump around the towns and rapidly growing region because we can no longer dig a hole in the ground?
“Where is the equity for the people in Ashburton who are having to pay? Not the farmers – the people in the town who will have to pay in the future to pump water across the Ashburton River so Tinwald can have safer water.
“Where was the democracy and where was the discussion?”
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand