Chapter 10: Freshwater

Freshwater in New Zealand

Water is essential to New Zealand’s social, cultural, and economic well-being. It is also a focal point for recreational activities and our outdoor-focused way of life. New Zealand has 425,000 kilometres of rivers and streams, almost 4,000 lakes that are larger than 1 hectare, and about 200 aquifers.

By international standards, freshwater in New Zealand is both clean and plentiful in supply. However, demand for water is increasing. At the same time, some aspects of water quality are getting worse in areas that are dominated by intensive land use.

River and lake water quality

Land-use impacts on river water quality

Rivers in catchments that have little or no farming or urban development make up about half of the total length of New Zealand’s rivers and have good water quality. Water quality is generally poorest in rivers and streams in urban and farmed catchments. This reflects the impact of non-point-sources of pollution in these catchments, that is, pollution that does not have a single identified point of origin, such as urban stormwater, animal effluent, or fertiliser run-off. The proportion of the total river length that is in farmed catchments is more than 40 times the proportion that is in urban catchments.

Nutrients in rivers

While the levels of nutrients (which, in excessive amounts, reduce water quality) in our most polluted rivers are only about half the average for all rivers reported by countries to the Organisation for Economic Co-operation and Development (OECD), nitrogen and phosphorus levels have increased over the past two decades. Nitrogen levels have increased most rapidly in rivers that are already nutrient-enriched.

Point-source pollution of rivers

Pollution from organic waste in rivers has reduced since the late 1980s. This indicates improved management of point-source discharges of organic waste, that is, pollution from a single facility at a known location, such as discharges from wastewater treatment plants, meatworks, and farm effluent ponds.

Nutrients in lakes

Two-thirds of New Zealand’s lakes are in natural or partially developed catchments, such as native bush, and are likely to have good to excellent water quality. Small, shallow lakes surrounded by farmland have the poorest water quality of all our lakes.

Water quality at swimming spots

Over the 2006–2007 summer, 60 per cent of the swimming spots on rivers and lakes that were monitored had low levels of bacteria, indicating that these sites have good water quality and are suitable for swimming. Ten per cent of the monitored swimming spots frequently had levels of high bacteria, indicating that they are generally unsuitable for swimming. Bacteria levels appear to have improved in our recreational waters over the past few years.

Groundwater quality

Sixty-one per cent of the groundwaters in New Zealand that are monitored have normal nitrate levels; the remainder have nitrate levels that are higher than the natural background levels, and 5 per cent have nitrate levels that make the water unsafe for infants to drink. Twenty per cent of monitored groundwaters have bacteria levels that make the water unsafe to drink. High levels of nitrates and bacteria are particularly common in shallow, unconfined aquifers. These aquifers are the most vulnerable to pollution from land-use activities, such as farming and urban development.

Freshwater demand

Abundance of freshwater

Because New Zealand has a low population and high average rainfall, it has more total freshwater per person than more than 90 per cent of almost 200 other countries around the world. However, not all of this water is in the right place at the right time; some areas experience a surplus or shortage of water.

Demand and allocation

It is estimated that total water use in New Zealand currently equates to two to three times more water per person than in most other OECD countries. Demand for water is increasing, particularly in areas that are already short of water. Drier parts of the country have the highest demand. For example, Canterbury accounts for over half of all water allocated in New Zealand; that is, the amount of water that is permitted to be used. Several eastern regions, including Canterbury and Ōtago, have surface water catchments that are highly allocated, so come under pressure during drier times of the year.

The allocation of water in New Zealand increased by 50 per cent between 1999 and 2006. This is mainly a result of an increase in the area of irrigated land. Irrigation now uses almost 80 per cent of all water allocated.

Present and future management

Because pollution of freshwater from point-source discharges is now largely controlled under the Resource Management Act 1991, attention of resource managers has turned to reducing non-point-source pollution from intensive land use. As a result, there is greater emphasis than in the past on managing intensively used land through stream-bank (riparian) planting, nutrient management, and excluding stock from waterways using bridging and fencing.

Water allocation and pollution caused by intensive rural and urban land use will continue to be the focus of freshwater management in New Zealand. Balancing the competing needs of water users – recreational users, town water suppliers, hydro-electricity generators, tourist operators, and farmers – is likely to become increasingly important.

New Zealand has 425,000 kilometres of rivers and streams, almost 4,000 lakes that are larger than 1 hectare (Ministry for the Environment, 2006c), and about 200 groundwater bodies (aquifers) (White, 2001).

Freshwater is among our most valuable natural assets. New Zealand’s rivers, streams, and lakes are a focal point of our national identity and outdoor way of life. They are highly valued for recreational activities such as swimming, boating, and fi shing, and are the centrepiece of some of the country’s best-known tourist destinations.

Clean and plentiful water provides us with a safe drinking supply, and also sustains the natural ecosystems that are home to many of New Zealand’s native species.

In addition, freshwater is a vital part of the New Zealand economy: it is used to irrigate crops and pastures, dispose of or dilute trade wastes and sewage, and produce hydro-electric energy (see chapter 5, ‘Energy’).

Water is also a fundamental taonga (treasure) for Mäori. Waterways are considered the arteries of Papatüänuku (Mother Earth) (Ministry for the Environment, 2005b). Mäori have cultural, historical, and spiritual links with many of the country’s springs, wetlands, rivers, hot pools, and lakes. They also value having healthy water bodies for mahinga kai (customary food and resource gathering).

By international standards, freshwater in New Zealand is both abundant and clean. Rainfall, which is the source of replenishment for our streams, rivers, lakes, and groundwater, is generally plentiful. With a population of just over 4 million and limited heavy industry, New Zealand’s human pressures on freshwater are relatively light compared with the pressures on such resources in many other developed countries.

However, protecting the country’s freshwaters is a growing challenge. With land-use practices becoming more intensive, particularly in farming, there is greater demand for water now than ever before, and evidence is building that its quality is declining in many water bodies.

Freshwater environments of New Zealand

New Zealand is a narrow, mountainous country characterised by relatively small catchments and fast-flowing rivers and streams. Half of its 425,000 kilometres of rivers and streams are small headwater streams.

Of New Zealand’s total length of rivers and streams, 51 per cent lies in catchments with predominantly natural land cover, such as native bush or alpine rock and tussock. The remaining 49 per cent of river length is in catchments that have been modified by agriculture (43 per cent), plantation forestry (5 per cent), or urban settlement (1 per cent).

New Zealand has 3,820 lakes that are larger than 1 hectare. Of these, 229 have an area greater than 50 hectares (Ministry for the Environment, 2006b). About 40 per cent of all lakes are in catchments in which the predominant land cover is pasture. Less than 2 per cent of lakes are in towns and cities (Ministry for the Environment, in press c).

The underground areas in which groundwater collects are known as aquifers. In New Zealand, the largest aquifers are porous gravels. Examples include the Heretaunga Plains in Hawke’s Bay and the Wairarapa, Manawatū, Canterbury, and Southland Plains. Other forms of aquifer include the fractured basalts of the Auckland region and the Coromandel Peninsula’s coastal sand aquifers.

Natural factors that affect freshwater

Three main natural factors influence the quantity and quality of freshwater in New Zealand: climate, topography, and geology.

Rainfall patterns vary across the country and between seasons. Generally, rainfall is much higher on the western side of both the North and South Islands, because the prevailing westerly winds pass over mountains that form the backbone of much of the country.

Rainfall is also higher in the winter than in the summer. This seasonal variation is more extreme on the east coast of both main islands, where summers are relatively dry, compared with on the west coast. Not only does rainfall control the amount of water that flows in rivers and aquifers, it can also affect water quality by carrying pollutants from the surface of the land to water bodies. The pattern of rainfall in New Zealand is expected to change in the future; the anticipated effects on freshwater quantity and quality are summarised in the box ‘More about climate change and freshwater’.

The shape and geology of New Zealand’s catchments also strongly influence water quality. Catchments that are steep-sided (such as those in mountainous regions) or made up of soft sediments are more prone to natural erosion. As a result, rivers draining from these catchments may carry high levels of sediment.

The type of rock and soil the water moves past and the time over which this interaction takes place also determine the characteristics of our freshwater. For example, groundwaters moving through volcanic rocks or geothermal areas are more likely to contain higher concentrations of minerals (such as sulphates and/or chloride) and metals (such as arsenic) than are fast-moving river waters.

Human factors that affect freshwater

The main pressures on freshwater quantity and quality are the growing demand for water to meet society’s various needs and pollution resulting from human activities on land.

Water quantity

Demand for freshwater resources is increasing as New Zealand’s population grows and more intensive forms of land use, particularly farming, become increasingly widespread. This is especially noticeable in drier regions, such as Canterbury, where relatively high volumes of water are needed to irrigate pasture.

Damming and diverting water to meet needs for power generation, irrigation storage, and human consumption can deplete flows in rivers and reduce groundwater levels. As well as having effects on water quality (described below), flow depletion can lead to insufficient water being available to meet the needs of downstream users.

Draining land to improve farming productivity or enable urban development also reduces the size of water bodies. The Waikato region’s shallow peat lakes are examples of lakes that have shrunk in size and number as the surrounding farmland has been drained.

Water quality

Figure 10.1 summarises the main sources of pollution in rivers, lakes, and groundwater. These are identified as point-sources and non-point-sources. Point-sources refer to discharges of pollutants from a single facility at a known location (for example, a wastewater treatment plant). Non-point-source pollutants do not have a single point of origin (for example, they may include pollutants that have run off wide areas of disturbed or developed land after rainfall).