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Overview

This chapter explains why the condition of our freshwater environment is important, and presents information about the pressures on New Zealand’s fresh water and how its state is changing over time.

Our freshwater environment – a summary

Fresh water is important to New Zealand’s way of life and economy. Our rivers, lakes, wetlands, and groundwater support the creation of wealth through agriculture, horticulture, hydroelectricity generation, and tourism. New Zealanders enjoy many forms of recreation in our lakes and rivers, including swimming, boating, and fishing. For Māori, fresh water is a taonga and essential to life and identity. Access to fresh water for food, materials, and customary practices is important to Māori. New Zealand’s fresh water supports a range of aquatic animals including crayfish and more than 50 fish species, 39 of which are indigenous to New Zealand.

The quality of water in New Zealand’s lakes, rivers, streams, and aquifers is variable, and depends mainly on the dominant land use in the catchment. Water quality is very good in areas with indigenous vegetation and less intensive use of land, and poorer where there are pressures from urban and agricultural land use. Rivers in these areas have reduced water clarity and aquatic insect life, and higher levels of nutrients and Escherichia coli (E.coli) bacteria.

Land use and population growth have placed increasing pressure on waterways. This is more evident with agricultural land because it surrounds 46 percent of New Zealand’s rivers. Between 1990 and 2012, the estimated amount of nitrogen that leached into soil from agriculture increased 29 percent. This increase was mainly due to increases in dairy cattle numbers (and therefore urine which contains nitrogen) and nitrogen fertiliser use. Once in the soil, excess nitrogen travels through soil and rock layers, ending up in groundwater, rivers, and lakes.

Between 1989 and 2013, total nitrogen levels in rivers increased 12 percent, with 60 percent of the 77 monitored sites showing statistically significant increases. The greatest impact of excessive nitrogen levels in New Zealand rivers is nuisance slime and algae (periphyton) growth. This growth can reduce oxygen levels in the water, impede river flows, and smother the riverbed and plant life, which fish and other aquatic animals depend on for food and habitat. About 49 percent of monitored river sites currently have enough nitrogen to trigger nuisance periphyton growth, as long as there is enough sunlight, phosphorus, and a lack of flood events for periphyton to bloom.

High levels of nitrogen can also be harmful to fish; however, less than 1 percent of monitored river sites have nitrogen levels high enough to affect the growth of multiple fish species.

Like nitrogen, excessive phosphorus also promotes the growth of nuisance periphyton. Most phosphorus enters rivers on eroded soil and settles on riverbeds. Dissolved phosphorus levels increased (worsened) in the large rivers sampled by NIWA between 1989 and 2013, with 51 percent of the 77 monitored sites showing statistically significant increases. In contrast, dissolved phosphorus levels decreased (improved) in a broader collection of rivers sampled by regional councils between 1994 and 2013, with 48 percent of the 132 monitored sites showing statistically significant decreases. About 32 percent of monitored river sites currently have enough dissolved phosphorus to trigger nuisance periphyton growth.

Water clarity is a measure of underwater visibility and affects our ability to use rivers for recreational activities such as swimming and fishing. Water clarity is lower (worse) in urban and pastoral (agricultural) areas, but improved at two-thirds of monitored sites between 1989 and 2013.

Improved phosphorus levels and water clarity in rivers over the past 20 to 25 years were likely to be due to several factors. These include the management of erosion along river banks and surroundings, tree planting near waterways, reduced effluent discharges from industry, and a decrease in phosphorus fertiliser from 2004 to 2014.

The primary risk to human health from poor water quality comes from faecal contamination. This is indicated by the presence of E.coli bacteria in rivers or lakes. E.coli levels are highest in urban and pastoral areas, which are usually within 20 kilometres of where people live, and where people like to swim during summer. Higher E.coli levels are indicative of higher risks of infection for swimmers, particularly from stomach bugs like Campylobacter.

E.coli levels in New Zealand rivers meet acceptable standards for wading and boating at 98 percent of monitored sites. The acceptable levels for swimming are more stringent and require more intensive management. This is because E.coli can spike to high levels in rivers and streams for 2–3 days after heavy rainfall or during low river flows, particularly in lowland areas. Regional councils frequently monitor popular swimming spots for health reasons. Information about these sites, and their suitability for swimming on a given day, can be found on the Land, Air, Water Aotearoa website.

New Zealand has plentiful fresh water but not always where demand is greatest. Total average annual rainfall is high enough to fill Lake Taupō nine times over, but less rain falls in the north and on the east coasts of the North and South islands. Fresh water is mainly taken from rivers, lakes, and groundwater for hydroelectricity generation and irrigation for intensive farming. The remainder is used for industry, town supply, and stock water. Water use varies by region, with about half of the national consumption occurring in Canterbury, and one-quarter in Otago.

How we measure freshwater quality

New Zealand’s lakes, rivers, and groundwater are monitored regularly by regional councils, NIWA, GNS Science, iwi, and community interest groups.

New Zealand’s river network has a total river length of 199,641 kilometres. Regional councils monitor river water quality to manage environmental impacts. These sites tend to be in catchments dominated by agricultural land use. For this report, we included up to 708 comparable regional council river sites in our assessment. Of these sites, about 65 percent are in pastoral areas, 27 percent in indigenous landscapes, 4 percent in urban areas, and 4 percent in exotic forest. Rivers in most areas, particularly low-lying and hilly areas in the North and South islands, are well represented, while mountainous areas in the South Island and parts of the central North Island are not well represented.

NIWA also monitors water quality at 77 other sites on 35 major river systems (see figure 21). Together, these 77 sites drain about half of New Zealand’s land and were selected to represent water quality in larger rivers (ie main-stem rivers) across New Zealand (Davies‐Colley et al, 2011). The sites are located in the lower and upper reaches of each river, with 52 percent of the sites in pastoral areas, 44 percent in indigenous landscapes, and 4 percent in exotic forest. The NIWA sites were established to monitor changing trends in water quality in larger rivers over time. The sites are mainly located in cooler wetter locations (eg Southland and the Manawatu). Rivers in cooler climates that experience dry or extremely wet conditions are not well represented (eg Fiordland and the Central Plateau). No measurements are taken in urban areas. As the same sites have been measured consistently since 1989, the data is particularly useful for tracking changes in water quality over time (Ballantine & Davies-Colley, 2014).

Regional councils and NIWA measure a range of parameters at each of the sites they monitor. The parameters include water clarity; levels of nitrogen, phosphorus, and E.coli; and the number and type of macroinvertebrates present (aquatic animals such as insects, freshwater crayfish, snails, and worms). Some macroinvertebrates are sensitive to pollution, and their presence or absence is a good indicator of the overall health of a river or stream.

We used the NIWA river sites to assess trends in water quality for the 25-year period from 1989 to 2013. As the median dissolved phosphorus concentrations were significantly higher at regional council sites, we also used these sites to assess dissolved phosphorus trends for the 20-year period from 1994 to 2013.

We assessed the current state of New Zealand’s rivers using the combined NIWA and regional council sites. When combined, these sites provide the broadest national coverage of river water quality.

Regional councils and NIWA also monitor lakes. Four percent of lakes are currently monitored, but this proportion includes many of the largest and popular lakes close to urban areas. Lake water quality is assessed using the trophic level index (TLI), which combines a number of water-quality parameters. TLI scores rise with increasing eutrophication (elevated nutrient levels that can promote excessive algae growth and reduce oxygen levels in the lake). For this report, 65 lakes are assessed.

GNS Science monitors groundwater at about 100 sites that are fairly evenly distributed throughout the country. The current state of groundwater and trends in groundwater quality (for the 15-year period from 1998 to 2013), were assessed using the GNS Science sites.

Iwi and hapū groups are the main sources of environmental information relevant to Māori. Some Māori communities monitor rivers, streams, lakes, and wetlands in their rohe (area). To measure the health of waterways, they use the cultural health index or other methods (such as the mauri compass) that have a mātauranga Māori perspective. Crown research institutes such as NIWA and Landcare Research also collect data of significance to Māori, including data on taonga fish species.

For more information see: Fresh water supports Māori well-being and identity section.

Figure 21:


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Note: National River Water Quality Network sites. Rivers are labelled where they enter the sea.

This map illustrates the river sites monitored by NIWA across New Zealand. Visit the MfE data service for the full breakdown of the data.