River Water Quality
This page defines water quality and links to reports on river water quality in Tasman.
The quality of water in our rivers is defined by how the physical, chemical and biological condition of the water and channel meets the needs of people and ecosystems. These conditions are influenced primarily by the climate, source of flow, geology and land use around a river.
Some of the most important indicators of water quality are:
- Faecal bacteria concentrations (the level of disease-causing organisms)
- The quantity of fine sediment (mud, silt and sand less than 2mm)
- Dissolved oxygen concentrations
- Nutrient concentrations (particularly nitrogen and phosphorus)
- Water temperature
- Water clarity
Why We Measure Water Quality
The monitoring of water quality in the district makes it possible to:
- Determine suitability for different uses. Water quality is frequently monitored to assess its suitability for a specific purpose, such as for swimming, as a source of drinking water, or as a habitat for fish and other aquatic animals.
- Assess adequacy of controls on discharges. Discharges of contaminants to water require resource consent from Council. When authorisations are given (usually as discharge consents) account is taken of the likely impact of the discharge on the quality of the receiving waters, based on knowledge of the water body at that time. Restrictions are placed on the discharge to limit any unacceptable water quality impacts. Additional monitoring improves our understanding of the resource and helps us to determine if those restrictions are still appropriate.
- Establish baseline water quality. To understand the impacts of human land use on river water quality, it is critical to have baseline sites. These sites are in rivers with a high proportion of native forest upstream.
- Detect long-term trends. An important question we can ask about our rivers is whether water quality at a particular place has degraded over time. Regular monitoring, over many years, allows for both degrading and improving trends to be detected.
- Meet the Council's legal responsibilities. Under the Resource Management Act 1991, local authorities, including the Tasman District Council, are required to monitor the overall state of the environment of their region. Section 35 states that Council must monitor the 'State of the Environment' to the extent “as is necessary to carry out effectively its functions”. This is important because it tells the Council and the wider community how successful we have been as a community in achieving the purpose of the RMA – the sustainable management of our natural and physical resources.
River Water Quality in Tasman
Tasman District is fortunate to have relatively few water quality issues compared to other parts of New Zealand, this is assisted due to the District’s large rivers having a significant proportion of native forest in their headwaters. Therefore, any inputs of pollutants from developed land in the middle and lower reaches are substantially diluted by the large volume of high quality water from upstream.
The main problems with water quality are currently found in small streams whose catchments contain a large proportion (>50%) of intensively developed land. The most common issues in these waterways are:
- High levels of disease-causing organisms, especially after rain;
- Too much fine sediment dirtying the water and filling the spaces between stones
- Low dissolved oxygen concentrations in summer
- High water temperatures in summer
The solution to many of the problems that remain is likely to be targeted streamside planting, which effectively addresses problems with dissolved oxygen levels (essential for the survival of fish and other aquatic life), water temperature, habitat removal and fine sediment trapping by aquatic plants.
The latest report on river water quality in Tasman:
Results of toxic algae monitoring are published on this page.