Kōrero: Water quality

Whārangi 5. Management of water quality

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Resource Management Act 1991

Water in New Zealand is protected by legislation, principally the Resource Management Act 1991. It provides a legal framework for using water, managing its quality, and balancing the needs of different groups who affect or use water. For example, fishers and swimmers want the lakes and rivers to be clear, while factory owners need to dispose of waste material.

Regional councils throughout the country monitor water quality, and then decide how to manage land and effluent. In consultation with the local community, a council might decide to maintain high water quality in upland rivers and lakes for recreation and biodiversity, but allow some runoff and waste into lowland rivers and estuaries.

Weeding the water

Harvesting (cutting and removal) is one way to control water weeds. This can improve water quality when unwanted nutrients are removed along with the weed.

Standards and guidelines

The Ministry for the Environment and regional councils, in consultation with the scientific community, has set water-quality standards and guidelines for water and its use.

There are set limits for the physical, chemical and biological factors affecting water quality. For example, dissolved oxygen is kept above 80% of saturation, to protect sensitive fish species. Standards vary according to how the water is used – for example, waters with E. coli counts of less than 260 per 100 millilitres may be fit for swimming or boating, but not for drinking.

Guidelines have the same purpose but are more descriptive (for instance, the absence of algal growths on rocks), and used only as indicators of changes in water quality.


Grass carp fish have proved to be useful at chomping through underwater plants that clog lakes and streams. They can be used for this purpose in New Zealand, if approved by the government and the Fish and Game Council. Grass carp are often confused with koi carp, which can seriously harm water quality. Koi carp can breed in the waterways, whereas grass carp are unlikely to do so.

Farm management

Establishing a link between farm runoff and reduced water quality in rivers or lakes can be difficult. Reducing the impact of farms on waterways has tended to be voluntary, rather than through strict regulations.

Farmers use a number of strategies to minimise effluent loss into waterways. Many dairy farmers now spray effluent from cowsheds onto paddocks, and some have set up wetlands that act as effluent treatment areas. These are managed to be effective over a long period. Unwanted nutrients are filtered and absorbed from the runoff water as it moves through, before it reaches defined waterways. Some regional councils have set limits on the amount of nitrogen fertiliser that can be used on dairy farms, particularly in sensitive catchments such as Lake Taupō.

Both industry and government agencies have a role in managing water quality from farmland.


The dairy company Fonterra Co-operative Group, regional councils, and the ministers for the environment and for agriculture and forestry have a voluntary accord. This aims to minimise the impact of dairying on New Zealand’s streams, rivers, lakes and natural wetlands so that they are suitable, where appropriate, for fish, drinking by livestock, and swimming. This will be done by keeping dairy cattle out of streams, lakes and wetlands, treating farm effluent, and controlling the use of fertilisers.


With the farming industry, the New Zealand Fertiliser Manufacturers’ Association has set up the Code of Practice for Fertiliser Use to reduce the ill effects of fertiliser on the environment. The code has guidelines for farmers and contractors on best practice.

Me pēnei te tohu i te whārangi:

Mike Scarsbrook and Kit Rutherford, 'Water quality - Management of water quality', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/water-quality/page-5 (accessed 22 July 2024)

He kōrero nā Mike Scarsbrook and Kit Rutherford, i tāngia i te 24 Nov 2008, updated 18 Jul 2016