To fully assess the state of the nation's water, the main indicators need to be measured in a regular and standardised way throughout the country. Progress toward this is now underway. Fortunately, a large amount of water monitoring is already carried out, both at the regional level and through several national programmes which focus on rivers, shallow lakes, groundwater and piped water supplies. Although their coverage, timeframes and monitoring methods vary, these data allow some general conclusions to be drawn.
From these it is clear that the pressures on our surface waters, coastal waters and groundwaters are intense enough in some areas to cause problems of scarcity, pollution and ecological degradation. However, some of these pressures are probably not as severe as they once were. Most point sources of pollution have become better managed over the last 20 to 30 years. Although urban sewage disposal is still a problem in some areas, very few communities now discharge untreated sewage into water and many are upgrading their treatment systems to better safeguard their rivers, lakes and beaches.
Drainage, dam construction, irrigation and flood control channelling have greatly altered the natural character of our waters. The surrounding land use changes have added to this, through vegetation clearance, run-off and sedimentation. Indigenous fish now live in fragmented habitats, as do wetland birds and plants. Maintaining the natural character of what remains is now identified in the Resource Management Act as a matter of national importance.
Non-point sources of pollution place the greatest pressures on water quality and have, so far, proven difficult to deal with because the solutions lie mostly in land management practices and lifestyle and consumption patterns (particularly our heavy use of motor vehicles). The most significant non-point sources appear to be agricultural run-off into waterways, leached nitrate into groundwater from horticultural and pastoral land, and urban stormwater which is a major source of contamination and debris in many coastal waters. The greatest impact of non-point source pollution is in lowland waterways, shallow lakes and shallow estuaries.
Much of the stormwater pollution in Auckland's estuaries has been attributed to urban runoff, particularly from motor vehicles, and is predicted to get worse.
Water quality is generally high around the coast, in the deep lakes, and in the headwaters of most rivers, and in many cases this is maintained into lowland areas. However, water quality deteriorates in streams, rivers and lakes which drain agricultural catchments, with agricultural run-off causing elevated nutrient and sediment loads. Microbiological contamination from the run-off of agricultural wastes also contributes to the poor condition of many small rivers and streams in agricultural catchments.
Coastal seawater is generally suitable for swimming and other forms of contact recreation. In areas away from urban sewage outfalls, stormwater outfalls and boat effluent, coastal water is also suitable for the gathering of seafood. However, the disappearance of seagrasses in estuaries and the proliferation of sea lettuce (a native seaweed) suggests that elevated nutrients and suspended sediments are affecting some of our estuarine and coastal ecosystems.
Pests and weeds are an increasing threat to freshwater and marine ecosystems. The impacts on people include the potentially negative economic and health effects of toxic algae. Our ability to respond to harmful invaders has been enhanced by recent legislation on new organisms and biosecurity and by improved coastal monitoring for toxic algae.
Nitrate contamination of groundwater beneath pastures appears to be a significant environmental issue. Many shallow aquifers beneath dairying and horticultural land, and beneath organic waste disposal facilities are now contaminated by nitrate at levels that exceed the maximum allowable value for drinking water, and that pose an increased risk of eutrophication to the nitrogen limited lakes of the central North Island. Very limited data indicate that other pollutants, such as toxic metals and even pesticides in some places, may be entering groundwater by seepage from landfills, waste disposal facilities and contaminated sites.
Although the quality of water in our rivers, lakes, estuaries and harbours has probably improved in the past twenty years as point sources of pollution have declined and better treatment systems have been adopted, the pressures from non-point source pollution, introduced species and environmentally harmful development have barely begun to be dealt with. Issues requiring ongoing attention include:
- protecting the natural character of water bodies and water margins (including wetlands, estuaries, and riparian vegetation on riverbanks);
- controlling drainage and degradation of wetlands;
- controlling non-point source pollution of lowland streams and shallow lakes;
- controlling nitrate pollution in groundwater;
- maintaining freshwater and marine ecosystems;
- continuing to upgrade water and waste treatment systems;
- continuing to upgrade drinking-water supplies;
- controlling introduced pests and weeds;
- improving data on aquatic ecosystems; and
- improving data on the quality of groundwater resources.