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:
We are continuously monitoring the quality of the water in our region. Reports are published periodically.
All environmental reports are available:
Monitoring water quality makes it possible to:
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:
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.
Ammonia in waterways comes from either wastewater or animal wastes (dung and urine). High levels of ammonia (greater than 2.20 g/m3) are toxic to aquatic life, especially fish. The level of ammonia in water should be less than 0.05 g/m3 to avoid impacting on the most sensitive aquatic life.
Recreation that involves a person immersing there head under water such as swimming, water skiing and whitewater kayaking.
Micro-organisms such as bacteria, protozoa and viruses that cause disease in humans. Disease risk level is indicated by the concentration of E.coli or faecal coliforms.
Dissolved oxygen is important for fish and other aquatic life to breathe. Water should be greater than 80 percent saturated with dissolved oxygen for aquatic plants and animals to live in it. Low levels of dissolved oxygen often indicates the presence of large numbers of aquatic plants, especially in small streams.
E. coli is a type of bacteria. It is used as an indicator of the human health risk from harmful micro-organisms present in water, for example, from human or animal faeces. Most E. coli strains are harmless, but some can cause serious food poisoning in humans.
A group of bacteria, that includes E.coli, found in the faeces of warm-blooded animals. Also used as an indicator of human health risk.
Filamentous algae grows in long (<2cm) strands on the stream bed. Such algae grows in greatest abundance in conditions of abundant light, nutrients and stable stream flow. If the total percent cover of this algae gets over 30%, then it is likely there are excessive nutrients discharging to the waterway.
Sand, silt and clay particles less than 2 mm in size. Fine sediment can be introduced to streams by natural processes (wind, water movement) or human activities such as agriculture, forestry and urban development.
Invertebrates are organisms without an internal skeleton such as insects, worms, shellfish and crustaceans. The 'macro' prefix means they can be seen without using a microscope.
Nitrogen is a nutrient that can encourage the growth of nuisance aquatic plants. These plants can choke up waterways and out-compete native species. High levels of nitrogen in water can be a result of run-off and leaching from agricultural land. Ideally, nitrogen levels in water should be less than 1.0 grams per cubic metre to prevent excessive growth of nuisance plants. Non-point sources of nitrogen are the major contributors of nitrogen to waterways.
Discharges of contaminants that do not come from a single place, such as an industrial site, or from a specific outlet, such as a pipe. Some sources of non-point source discharge include run-off from agriculture, forestry and urban areas (for example, stormwater and construction sites).
Discharges of contaminants that come from a stationary or fixed facility, for example, from a pipe, ditch or drain.
pH is a measure of the acidity or alkalinity of water. A very high or very low pH means that water can be toxic for aquatic life. The pH range that is suitable for aquatic plants and animals is 6.5 – 8.5. In Tasman District pH is very seldom an issue.
Phosphorus is a nutrient that can encourage the growth of nuisance aquatic plants. These plants can choke up waterways and out-compete native species. High levels of phosphorus in water can be a result of either wastewater, or, more often, run-off from agricultural land. Ideally, phosphorus levels in water should be less than 0.01 grams per cubic metre to prevent excessive growth of nuisance plants.
Water that runs off the surface of the land, and flows into waterways. Run-off may contain sediment, nutrients or faecal matter.
Water temperature is important for fish spawning and aquatic life. Between May and September, when trout are spawning, water should be less than 12°C. Between October and April, water should be less than 20°C for general trout health and less than 25°C for most native fish. Stream water temperatures are affected by climate, season and the amount of shading along the stream.
Turbidity is a measure of the murkiness of water, reflecting the amount of fine sediment in the water. High turbidity reduces the amount of light available to the plants and animals living in the water. It reduces the ability of plants to photosynthesise. It also makes it difficult for fish and other animals to see their prey.
Water clarity and underwater visibility is important for recreation such as swimming and waterskiing. It is also important from an aesthetic point of view – most people prefer to see clear water in our rivers and streams. To allow good visibility for swimming, you should be able to see at least 1.6 metres underwater.
Water clarity is measured by sighting a black disc attached to a tape measure, using an underwater viewing box.