Water pollution in New Zealand is an increasing concern for those who use and care for waterways and for New Zealand regulatory bodies. An increase in population is linked to an increase in water pollution, due to a range of causes such as rural land use, industrial use and urban development. Fresh water quality is under pressure from agriculture, hydropower, urban development, pest invasions and climate change. While pollution from point sources has been reduced, diffuse pollution such as nutrients, pathogens and sediments development and from stormwater in towns is not under control. There are more than 800 water quality monitoring sites around New Zealand that are regularly sampled.
, Auckland is the region with New Zealand's most polluted waterways, with 62% of rivers and lakes graded poor by the Ministry for the Environment for swimming, and 0% of rivers and lakes graded as good.
In 2018, waterways across New Zealand have been showing improvements across a number of water quality measures, as monitored by LAWA data.
Water quality guidelines
Guideline standards for water quality are published by MfE.
Water pollution by sector
Agriculture
Agriculture is a major use of lowland areas of New Zealand and has affected water quality. The expansion of intensive dairy production has resulted in greater levels of nitrogen in soil, surface and groundwater.
In 1993, the National Institute of Water and Atmospheric Research summarised available data on the quality of water in rivers. They concluded that "Some lowland river reaches in agriculturally developed catchments are in poor condition" reflecting "agriculturally derived diffuse and point source waste inputs in isolation or in addition to urban or industrial waste inputs". The key contaminants identified in lowland rivers were dissolved inorganic nitrogen, dissolved reactive phosphorus, sediment and coliforms. Small streams in some dairy farming areas such as the Waikato and Canterbury were identified as being in relatively poor condition.
Sediment from erosion of hills and river banks is also a source of pollution of waters. The sediments loading from high intensity, increasing frequency storm and high rainfall events has led to millions of tonnes of sediment changing fluvial systems in NZ waterways. This sediment contains high organic contents from forest litter which is changing sedimentation patterns and increasing organic bed loads and deposition in NZ lakes and shallow coastal waters.
Since 2005 increased dairy farming rates of grazing animals have outstripped riparian planting and the ability of some Regional councils to manage and mitigate impacts on the quality of water, and there is some evidence of urea use leading to nitrogen levels in waterways. Horticulture, arable farming and plantation forestry generally have less effect than dairy farming.
In 2001 Fish and Game New Zealand started the high-profile dirty dairying campaign to highlight the effect of pollution from farming intensification on the ecological health of freshwater environments. As a reaction to this campaign Fonterra, the largest dairy company in New Zealand, along with a number of government agencies instigated the Dairying and Clean Streams Accord to address water pollution due to dairy farming. The aim of the Accord is to limit the access of stock to waterways. Fonterra exports the majority of its produce, and encourages farmers to limit environmental impacts as a method of getting environmentally aware consumers to purchase their products. The increase in research into sustainable farming and reducing fertilizer use, increasing the planting of native shrubs, grasses, flaxes and trees along the margins of streams. These techniques help intercept run off of manure, sediments and fertilizer and use them to enhance growth of the planted zones.
Over the past decade, regional councils have increasing imposed more regulatory requirements on farmers to reduce their environmental impacts. A number of councils - including Environment Canterbury, Horizons Regional Council and Hawke's Bay Regional Council require most farms to have Farm Environment Plans in place, with some farms in Otago and Waikato also required to have Farm Environment Plans in place. The plans require farmers to manage environmental risks around activities such as farm dairy effluent, erosion, discharges into waterways (through planting and fencing intensively stocked areas), irrigation and the application of nutrients. Some councils have also imposed nutrient limits on farmers.