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Water quality glossary

This glossary explains some of the technical words used when assessing water quality.

ecology icon

Ecological measures

Dissolved oxygen

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 in Waikato rivers often indicate the presence of large numbers of aquatic plants, especially in small streams.

pH

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 to 9.

Turbidity

Turbidity is a measure of the murkiness of water, reflecting the amount of suspended 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. Turbidity should be less than 5 NTU (turbidity measurement scale) for water to support plant growth.

Total ammonia

High levels of ammonia are toxic to aquatic life, especially fish. The level of total ammonia in water should be less than 0.88 grams per cubic metre to be safe for fish. Ammonia in waterways comes from either waste waters or animal wastes (dung and urine).

Temperature

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. Water temperature is affected by climate and by discharges of cooling water from industry. Temperatures are naturally higher in the northern Waikato than in streams near Taupo.

Total phosphorus

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 waste water or, more often, runoff from agricultural land.

Ideally, total phosphorus levels in water should be less than 0.04 grams per cubic metre to prevent excessive growth of nuisance plants. Waikato Regional Council considers that rivers and streams with total phosphorus levels above 0.04 grams per cubic metre are undesirably nutrient-enriched. Three-quarters of all measurements from the New Zealand national rivers programme have phosphorus levels below this value.

Total nitrogen

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 runoff and leaching from agricultural land.

Ideally, total nitrogen levels in water should be less than 0.5 grams per cubic metre to prevent excessive growth of nuisance plants. Waikato Regional Council considers that rivers and streams with total nitrogen levels above 0.5 grams per cubic metre are undesirably nutrient-enriched. Three-quarters of all measurements from the New Zealand national rivers programme have nitrogen levels below this value.

Swimming icon

Human recreational use measures

Baseflow clarity

Water clarity and underwater visibility is important for recreation such as swimming and water-skiing. 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.

Clarity is measured using a black disc attached to a tape measure, and an underwater viewing box. It is measured in rivers during baseflow. Baseflow is defined as flows below the upper decile flow. This is because most people don’t swim during high or flood flows, which always contain higher levels of sediment from runoff.

Escherichia coli (E. coli)

E. coli bacteria have been used as an indicator of the human health risk from harmful micro-organisms present in water, for example from human or animal faeces.

Median

The median number of E. coli bacteria present in water samples should be less than 126 per 100 ml of water if it is to be used for recreation.

Single sample

The maximum number of E. coli bacteria present in any single water sample should be less than 550 per 100 ml of water.

Leaching

A process by which chemicals in the soil (especially the plant nutrient nitrogen), are moved out of the soil by water.

Non-point sources of nitrogen are the major contributors of nitrogen to waterways.

Point source discharges

Discharges of contaminants that come from a stationary or fixed facility, for example from a pipe, ditch or drain.

Check out the Operative Waikato Regional Policy Statement definition.

Non-point source discharges

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 runoff from agriculture, forestry and urban areas (for example stormwater and construction sites).

Check out the Operative Waikato Regional Policy Statement definition.

Runoff

Water that runs off the surface of the land, and flows into waterways.

Runoff can contain:

  • Sediment.
  • Phosphorus.
  • Faecal matter – bacteria and viruses.
  • Nitrogen – but most nitrogen enters waterways through leaching.

Site average

The site average is the average value of the proportions found to be 'excellent', 'satisfactory' and 'unsatisfactory' for each of the relevant variables (seven variables for ecological health, and two for swimming).