Canterbury’s Ticking Time-bomb Over Water Nitrate Levels

New Zealand Federation Of Freshwater Anglers (Inc.)

Press release

Canterbury’s Ticking Time-bomb Over Water Nitrate Levels

A trout and salmon angling advocacy group has issued a stern warning over Canterbury’s water having excessive nitrate levels which are toxic to both aquatic life and human health.

Dr Peter Trolove president of the NZ Federation of Freshwater Anglers (NZFFA) said a recently released study of 2011 – 2020 ten year trends in Canterbury’s groundwater quality, released by Ecan in July 2021 were alarming.

“Basically they show no evidence that Ecan is a credible manager of Canterbury’s groundwater,” he said. “The Ministry for the Environment, on receipt of this report, should take note of Ecan’s inadequate performance and take some overdue corrective action(s).”

Excessive nitrate levels are toxic to young trout and salmon and native fish, while overseas studies have shown a strong link between high nitrate levels in drinking water and bowel cancer in humans. Bowel cancer is the second-highest cause of cancer death in New Zealand while a Danish study of 2.7 million people has shown a strong link between nitrate levels and the disease. Recent data show also that drinking water supplies in some parts of New Zealand have nitrate levels more than three times higher than the threshold level for colorectal cancer risk identified in the Danish study.

, Canterbury’s Ticking Time-bomb Over Water Nitrate Levels
NZFFA Nitrate Testing Kit with Timaru DC Warning

In addition, high nitrate levels in water have a link to human birth problems such as underweight and premature babies.

New Zealand has one of the highest bowel cancer rates in the world while South Canterbury has double the national average. Excessive nitrates in rivers and underground aquifers is largely due to intensive and widespread dairy farm runoff and leaching. However, Dr Trolove said a number of NZ family dairying farmers he had spoken to were deeply concerned. He also pointed out the source of nitrates was not just dairying in itself but meat plants and dairying processing industry often owned by corporate Japanese and Chinese interests.

, Canterbury’s Ticking Time-bomb Over Water Nitrate Levels
TDC issues the first Nitrate warning signs

“Don’t hang this just on farmers, particularly the Kiwi ones. They are alarmed what national and local politicians have allowed to happen,” he said.

NZFFA’s Dr Trolove said Ecan’s costly and unverified farm environment plans based on the OVERSEER model have proved to be ineffective, despite being the key management tool of the Canterbury Water Management Strategy since 2010. Ecan does not appear to have any other tools to meet its statutory obligation under the RMA (1991) to maintain or enhance Canterbury’s freshwater quality, quantity and ecosystems.

With regard to nitrate pollution, the Annual Groundwater Quality Survey 2020 found 118 of 322 wells are “very likely” or “likely” showing increasing trends in nitrate pollution, 20 of 322 wells do not meet the NZ Maximum Allowable Values (MAV) for drinking water and 114/ of 322 wells have over 1 mg/L NO3-N he said. 

“In 2021 Ecan justified a rate increase of 24% in order to manage freshwater. How credible is that?” he asked.

NZFFA has been conducting monthly nitrate testing of surface waters in the lower Selwyn Water Zone and less frequent testing in the Ashburton and Hinds Water Zones. In collaboration with Greenpeace, NZFFA has tested over 400 well samples in the Waimakariri, Selwyn, Ashburton and Temuka Water Zones. Ten wells in Ashburton and six in Temuka exceeded the MAV (11.3%). The Timaru District Council is presently providing tanker loads of potable water to the Rangitiata Huts Community due to water above the MAV for nitrate

“NZFFA testing has now found five Canterbury streams or rivers including two trout bad salmon hatchery streams with nitrate levels over 7.0 mg/L NO3-N. The Selwyn River reached 9.87 mg/L in 2021, while Hart’s Creek remains stubbornly above 8.0 mg/L. Two large coastal drains in the Hinds Water Zone exceeded the New Zealand MAV for drinking water of 11.3 mg/L NO3-N.”

Not only has the freshwater ecosystem being threatened but human health with tragic results also said Dr Trolove.

“How long can central and local government idly sit on their hands in the face of this tangible evidence,” he said.

Some local body & Ecan councillors, and farmers with a pecuniary interest in continuing their pollution of groundwater appear to show an appallingly heartless attitude to the environment and public health.  

 “So what?”, “This is a legacy issue”, “The public will have to learn to live with it”, “I don’t  understand the science”, are dismissive comments that have been made in the media or directly to Dr Trolove. 

Dr Trolove described the nonchalance as “irresponsible and heartless.”

“How many times do we have to have these reports of the critical and worsening situation at the expense of the ecosystem and human health, before we get some action,” he said.

Contact: Dr Peter Trolove, President NZFFA 029 779 0295 or 03 324 2779

C:\Users\andi\AppData\Local\Microsoft\Windows\INetCache\Content.Outlook\OYNWA3D8\DSC_1526 (002).JPG
Ocean View Road Lowcliffe- this is where a surface drain > than the MAV  for nitrate for drinking water discharges into the sea, coming from highly polluted groundwater from the Hinds plains.


Nitrate and NO3-N are not the same. The conversion factor is roughly 4.4
For example a nitrate limit of 50 mg/L equates to 11.3 NO3-N  (The US rounds this to have a drinking water MAV of 10.0 mg/L NO3-N).

NZ’s standard is based on the WHO recommendations set at 11.3mg/L nitrate-nitrogen. This is equivalent to a nitrate level of 50mg/L

From Aarhus University, Denmark – “We found statistically significant increased risks at drinking water levels above 3.87 mg/L, well below the current drinking water standard of 50 mg/L”

Denmark has a drinking water standard of 50mg/L for nitrate, which is equivalent to 11.3 mg/L nitrate-nitrogen.

Converting Aarhus University’s increased risk at 3.87 mg/L Nitrate to NZ’s Nitrate-Nitrogen suggests elevated risks to human health at 0.87 mg/L.

Further reading:

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5 Responses to Canterbury’s Ticking Time-bomb Over Water Nitrate Levels

  1. Dave Rhodes says:

    Hang on here
    Reading the footnote about research from Aarhus University’s increased risk of colorectal cancer at 0.87 mg/L NO3-N whereas Godzone has a limit set at 11.3 mg/L NO3-N.

    Probably no one in South Canterbury has drinking water of such purity – no wonder cancer rates are double the national average.
    This is scandalous and needs shouting from the rooftops – Greenpeace is asking for 1 mg/L but even that doesn’t seem safe enough.

    NZFFA - New Zealand Federation of Freshwater Anglers

    • Charles Henry says:

      So 11.3mg v 0.87mg implies we have standards set roughly 13 times the safe limits shown to us by research.
      Doesn’t this government and Ardern repeatedly say “follow the science”? If so, why are they not fulfilling any of their promises from 2017, not to mention their fiduciary duties to keep New Zealander’s safe from harm!

  2. Greg Kemp says:

    Interesting table below – seems many of our rivers are worse than the Yangze River – the most nutrient polluted in the world – Yeh Right

    NZFFA - New Zealand Federation of Freshwater Anglers

  3. Alan+Rennie says:

    AS for no going backwards , the NZ govt has already gone backwards in its human drinking water standards. The only NZ Drinking Water Standards ever signed off by the World Health Organisation was the first one prepared by our Health Ministry in 1984. Appropriately there was no level allowable for 1080 or nitrate residue in our children’s drinking water.

    The U.S. recognises the physical size difference of our society’s most vulnerable and have some lower “Maximum Allowable Values” for certain poisons for children. NZ Ministry of Health base all their figures on a 70kg adult.

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