How does dairy farming affect waterways?

In 2013, a report on water quality was released by the Parliamentary Commissioner for the Environment. For the dairy industry it was rather damaging as it proved a clear link between dairy intensification and declining water quality. In this article, we’ll discuss what the problem really is and how we can work towards mitigating it.


Let’s start with a positive note. While dairy farming is a contributor to declining water quality it is not the only one. All agricultural industries carry some responsibility and where the dairy industry has been regulated to help mitigate declining water quality, no such regulations exist for beef, sheep or deer farming. Other land and river-based industries (eg. forestry) are also key polluters. Invasive species of fish and plants are still a major problem. Climate change is also having a seriously harmful effect heating up our waterways. And even city living has a massive impact with contaminants coming out of the air, off roofs etc. and washing into the waterways. A recent opinion piece that ran on Stuff quotes data that says humans each contribute an average of 249 litres of treated waste per day to water, but dairy cows contribute an average of just six litres of effluent per day, only 3% of equivalent human waste by volume.

The answer really is for all Kiwis to adopt a “we’re all in this together” attitude. But now, let’s look at it from a dairy perspective. 


The main contaminants causing water pollution are:

  • Sediment - fine material from deforestation
  • Nutrients - nitrogen and phosphorus from livestock urine and fertiliser
  • Bacteria - E. Coli from animal faeces

Sediment is an issue because it washes into waterways, clogging them up and making them brown and dirty, and coating the river/stream bed with silt that then cuts it off as a habitat.

Nitrogen and phosphorus, while valuable nutrients on land to help plants grow, in large quantities in water cause excessive growth of weeds, algae and slime, as well as affecting insects, fish and water birds.

E. Coli comes from the faeces of livestock, and can be major health hazard. Remember the E.coli outbreak in Hawke's Bay in 2016? Bacteria like this are what is stopping people from being able to swim in rivers.


Cow urine contains high levels of nitrogen. When they piddle on the paddock, it’s too much nitrogen for the grass to be able to benefit from so it seeps down into the ground water, which then makes its way to the streams, rivers and lakes. What also makes nitrogen so difficult to control is that in the form of nitrate it’s highly soluble. 

Sediment gets into the water during/after it rains, while animal faeces comes from allowing the livestock direct or close access to the waterway. 


In 2013 DairyNZ implemented the 'Sustainable Dairying: Water Accord' as a kind of “blueprint” for protecting waterways on farmland. Many farmers are following this but it will likely be many years before huge improvements are noticeable. Some other actions are:

  • Building modern effluent systems and repurposing it to fertilise pastures.
  • Fencing off waterways from livestock and bridging crossings.
  • Riparian planting helps to protect waterways by absorbing dangerous nutrients from cow urine and fertiliser. It also helps hold soil together to stop sediment from washing into the water.
  • Change the cow’s diet to help reduce the nitrogen levels in their urine.
  • Experiments and research is being done into different types of grasses that can better absorb nitrogen before it seeps into the soil.
  • Off-paddock cow housing such as the options offered by a Dairy Barn System are proving to be a great way of managing nitrogen levels in soil as they provide a contained effluent management system as they get the cows off the pasture.
  • Using LowN sires in herd breeding programmes.

Read more ways of helping to reduce your footprint in one of our recent blog articles.


Some rivers are slowly improving. In a four part series produced by Radio Live, findings from a 2016 paper published by NIWA's chief scientist of freshwater and estuaries Dr John Quinn suggest that 500 out of 900 sites monitored tended to show signs of improvement with regards to phosphorus, ammonia and visual clarity, while up to half showed improving trends in E. coli contamination.