Water pollution in Aotearoa

Intensive dairying is the main cause of water pollution in New Zealand.

Over the past 30 years, Aotearoa’s dairy herd has nearly doubled. Some regions, like Canterbury, are seeing even more extreme increases in cow numbers. The combination of excessive cow numbers and a 693% surge in synthetic nitrogen fertiliser use has led to heightened climate emissions, polluted rivers, and increasingly contaminated drinking water.

The water pollution caused by intensive dairying is so bad that it takes a staggering 11,000 litres of water to dilute the pollution from just 1 litre of dairy milk produced in Canterbury. This is why increasingly, Canterbury’s water is becoming undrinkable, and its lakes and rivers are more and more unsafe for swimming.

This wasn’t an accident, and politicians of all political stripes are to blame. Regional councils set regional land and water plans and approve resource consents, and the Government sets national policy statements for freshwater management – both of which have been too permissive for decades, which has enabled dairy expansion and the subsequent degradation of lakes, rivers and drinking water.

Yes, drinking water is affected by pollution from the intensive dairy industry.

In New Zealand, up to 15% of people could be drinking water that is contaminated with potentially unsafe levels of nitrate. This number is even higher in rural communities. At the end of 2024, a shocking new report revealed that rural children are twice as likely as the average New Zealander to be exposed to dangerous levels of nitrate contamination in their school drinking water.

High levels of nitrate have been shown to increase risks of harm to human health, like increased risk of cancer and pregnancy complications.

Greenpeace’s Know Your Nitrate map outlines levels of nitrate pollution in drinking water across the country based on a combination of Greenpeace testing and local council testing. You can view the Know Your Nitrate map here.

Other contaminants like E. coli and campylobacter also threaten drinking water. In 2016, Hawke’s Bay experienced a devastating outbreak of the waterborne disease, campylobacteriosis, that resulted in many becoming seriously unwell. It is also believed to have contributed to four deaths. This was later found to have been caused by sheep effluent ending up in drinking water supply.
It is predicted that drinking water contamination as a result of the intensive dairy industry will get worse over the coming decades.

The impacts of water pollution on people can include:

1. High levels of nitrate can cause harm to human health, like increased risks of cancer and pregnancy complications.

New Zealand’s legal limit for nitrate in drinking water is set at 11.3 mg/L – there is a risk of infants developing Blue Baby Syndrome if they are fed formula that has been mixed with water at this level of nitrate contamination. However, recent studies have shown that there are increased risks to human health from exposure to nitrate at much lower levels – as low as 1 mg/L.

Studies have shown that up to 15% of New Zealanders could be drinking water with levels of nitrate contamination that could increase the risk of developing bowel cancer. And when nitrate levels reach 5 mg/L, the New Zealand College of Midwives has advised that pregnant women should consider seeking an alternative source of drinking water.

2. Polluted and unswimmable rivers mean that we can’t swim or fish in the waterways in our neighbourhoods.

The quality of New Zealand’s lakes and rivers has been in decline for many years. Several lakes in Canterbury are at risk of ‘flipping’ – of becoming so polluted that they cannot sustain plant and animal life. Of New Zealand’s many rivers, almost two thirds are degrading in quality. Every summer, we see more and more warnings of toxic algal blooms or unsafe levels of E.coli, meaning that it is unsafe to swim or fish in those rivers. This leads to people feeling increasingly disconnected from nature.

This is even more significant for tangata whenua, who have important ancestral and spiritual connections to freshwater lakes and rivers. For example, the Ōtūwharekai/Ashburton Lakes – an important seasonal mahinga kai area lying on the route between the east and west coasts – are at risk of flipping. The loss of mahinga kai like these lakes can result in tangata whenua experiencing a loss of connection to their whakapapa and cultural heritage.

Water pollution impacts on animals can include:

1. Eutrophication, where the water receives an excessive amount of nutrients, especially nitrogen and phosphorus, can lead to lakes and rivers no longer being able to support New Zealand’s native fish. That’s because their biological safe zone is very limited – if the amount of a certain nutrient in the water exceeds what they can tolerate, they will die. For example, New Zealand’s native fish can generally only tolerate a very low level of nitrate.

2. If the bugs and fish that live in and around the lakes and rivers die off, or can no longer tolerate the conditions, that impacts the birds that prey on these animals, and can lead to starvation. Lake Heron – so named for the kotuku or white heron that was once so common in the area – no longer sees the same high numbers of these birds, because there simply are not enough fish for them to live on.

3. Fish can suffocate as a result of large algal blooms. While many organisms cannot survive when there are excess amounts of nutrients such as nitrogen and phosphorus in the water, algal blooms thrive. When these algal blooms die off, oxygen is consumed in the process. This can create ‘dead zones’ where there is not enough oxygen, so the fish suffocate.

4. Irrigation schemes reduce the flow of water in rivers, which means that in the summer they often dry up, leaving fish to die.

Intensive dairying is a model of farming that crams as many cows as possible onto the land, in order to produce as much milk as possible. It uses significant amounts of inputs like synthetic nitrogen fertiliser, imported feed, and irrigation, to sustain these cattle, as the land cannot naturally sustain so many cows.

Intensive dairying is pushed onto New Zealand farmers by the intensive dairy industry. The intensive dairy industry is led by Fonterra, but includes all of the big corporations who profit off of the dairy sector in Aotearoa. It also includes big corporate mega-farms, which are often owned by overseas investors.

For more about our nitrate testing programme – including where our next water testing events will take place – click here.

You can get a free mail-in testing kit at any time here.

Check out our FAQs on nitrate contamination and nitrate testing results.

If you would like to speak to someone further about what your nitrate test result means, or if you would like to learn more about our work to ensure healthy drinking water for all and how you can be involved, please get in touch with us at  [email protected]