How healthy are our rivers?

On this page:

What affects stream health? •
How we manage water quality •
How we measure water quality •
How we assess stream health •
Glossary of water quality terms

What affects stream health?

Our rivers and streams have changed dramatically since European settlement. They’ve been dammed, had water pumped out or diverted, waste discharged into them, and exotic plants and animals introduced.

The land draining into these rivers (their catchment area) has been cleared for agriculture, forestry and urban development. These activities all increase the amount of runoff entering rivers and streams.

Many of our rivers and streams are in better condition now than they were in the 1950s, but they continue to be affected by pollution from a variety of sources, including runoff and leaching from agricultural land, stormwater and industrial discharges.

How we manage water quality

Managing water quality and aquatic life is a high priority for Waikato Regional Council. Clean water is vital for both ecosystems and our economy, so we measure water quality every month at 100 river and stream sites in the region, including five sites on the Waipā River, and 10 sites on the Waikato River.

We also survey stream habitat at 125 river and stream sites, including the plants, insects, fish and other animals that make up stream life in the Waikato region.

Image - staff monitoring water quality 860 x 282

How we measure water quality

Water quality is measured by either taking measurements on site or taking samples of water back to the laboratory for analysis.

How water quality is assessed depends on its use. Water suitable for some uses may be unacceptable for others. For example, water contaminated with treated sewage may be unsafe for swimming but still suitable for industrial cooling.

Aspects of water quality

The table below lists the different aspects of water quality we measure every month. It summarises why these are important and the guidelines used to assess them.

The water quality measures are divided into two groups:

ecological health - those measuring whether water quality is suitable for plants and animals living in a river
human use - those that measure whether water quality is suitable for human use and activities such as swimming. This is also called swimmability.

Our guidelines are based on national standards and guidelines.

Aspects of water quality monitored by Waikato Regional Council

Water quality variable (units)	Relevance	Categories
Water quality variable (units)	Relevance	Excellent	Satisfactory	Unsatisfactory
Dissolved oxygen (% of saturation)	Oxygen for aquatic animals to breathe	>90	80–90	<80
pH (acidity)	Can affect plants and fish	7–8	6.5–7 or 8–9	<6.5 or >9
Turbidity (NTU)	Can restrict plant growth	<2	2–5	>5
Total ammonia (g N/m³)	Toxic to fish	<0.1	0.1–0.88	>0.88
Temperature (°C)	Fish spawning May-Sep	<10	10–12	>12
Temperature (°C)	Fish health Oct-Apr	<16	16–20	>20
Total phosphorus (g/m³)	Causes nuisance plant growth	<0.01	0.01–0.04	>0.04
Total nitrogen (g/m³)	Causes nuisance plant growth	<0.1	0.1–0.5	>0.5
Human uses - recreation
Baseflow water clarity (m)	Visibility	>4	1.6 – 4	<1.6
Escherichia coli, single sample (no./100 mL)	Human health	<55	55 – 550	>550

How we assess stream health

Our staff have surveyed stream habitat and invertebrate communities (such as insects, crustaceans and worms) at more than 341 river and stream sites in the Waikato region since 1994.

A wide variety of native and exotic fish, invertebrates, aquatic plants and algae are found in Waikato rivers and streams. The number and type of species found at each site provides an indication of stream health. Over 130 different types of invertebrates have been identified in Waikato Regional Council's ecological monitoring of streams programme.

Studies show that invertebrates differ in their tolerance to pollution and habitat quality. Habitat quality can vary naturally, for example through differences in channel gradient and streambed substrate size, as well as through people-induced factors such as clearance of riparian vegetation. Plants and animals living in the stream may also accumulate contaminants over time. Even though present at a contaminated site, they may not be as healthy as the same species living in less stressful conditions.

The types of invertebrates that are present in a sample enable us to calculate biological indicators that reflect overall stream health.

Glossary of water quality terms

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

More information

River and stream water quality monitoring

We regularly monitor and report on river and stream water quality for ecological health and human contact recreation (for example, swimming).

Resource consents

Waikato Regional Council manages and requires the monitoring of resource consents to take water or discharge waste water to rivers, or to dam or divert rivers and streams. Tracking changes in water quality assists policy making and consent decisions.

Policies and plans

The Waikato Regional Policy Statement and Waikato Regional Plan provide objectives, policies and rules to manage the quality and quantities of water in our rivers and streams. We're also constantly reviewing our policies and rules.