River & stream quality 2001/02

Key points:

• The water quality in the upper reaches of our streams and rivers was good.
• Water flowing through agricultural areas was being polluted by runoff from the land.
• Water flowing through urban areas was being polluted by runoff and stormwater.
• Major improvements in water quality have occurred in the Ngarara Stream and Wainuiomata River.
• Discharges from municipal sewage treatment ponds are still polluting rivers in parts of the Region.

Monitoring water quality

Greater Wellington - The Regional Council monitors water quality at 51 sites in streams and rivers throughout the Region. We want to know if the water is okay for swimming and whether or not the aquatic ecosystem is healthy.

By improving our understanding of changes in water quality, and the reasons for these changes, we can become better at managing our rivers and streams.

Biological monitoring

We examine populations of macroinvertebrates at our water quality monitoring sites. Macroinvertebrates are animals without backbones that are large enough to be seen without magnification, like insects. The types of macroinvertebrates present, and their abundance, tell us if the stream is healthy. The map above shows the results of the biological data collected over the summer of 2001/02. You can see which rivers had the healthiest aquatic ecosystems and best water quality.

Physical and chemical monitoring

Physical and chemical monitoring of water quality is carried out monthly throughout the year. We measure things like temperature, issolved oxygen, pH and the levels of nutrients in the water.

Water quality at most sites was similar to previous years, but there was a big improvement in the Ngarara Stream and the Wainuiomata River. These water bodies have had some of the poorest water quality in the Region because treated sewage was being discharged into them. The sewage discharges to both rivers ended in December 2001.

The graph shows phosphorous levels in the Wainuiomata River between July 2000 and June 2002. Phosphorous is essential for plant growth, but if concentrations are too high, excessive growth may choke waterways.

How are we doing?

• The best water quality and stream health was in streams and rivers in the Tararua and Rimutaka Ranges, including the upper reaches of the Otaki, Hutt, Waiohine, Waikanae, Wainuiomata and upper Ruamahanga rivers.
• Mild to moderate pollution was found in streams and rivers flowing through agricultural land, including the Mangaroa, Tauherenikau, Waipoua, Mangatarere and lower Waiohine and Ruamahanga rivers. Runoff from farms, and stock walking and grazing in the rivers and streams, causes this pollution.
• The poorest water quality and stream health was found in streams and rivers flowing through urban areas, including the Karori, Porirua, Ngauranga, Owhiro and Waiwhetu streams, and the middle reaches of the Wainuiomata River. This was caused by polluted water entering streams and rivers from stormwater drains, especially after rain.

Suitability for swimming

Water quality at popular swimming sites is monitored weekly between November and March and assessed using national water quality guidelines for swimming. Water quality in the Region's western rivers was generally good. The Birchville and Boulcott sites on the Hutt River, and the Greenaway Road site on the Waikanae River, were the worst performers. Each was unsuitable for swimming on four occasions.

In the Wairarapa, water quality in the Waiohine, Waingawa and upper Ruamahanga rivers was good. All sites on the lower Ruamahanga River (downstream from Te Ore Ore) were unsuitable for swimming on numerous occasions. This was most common during November, December and January when the effects of pollution would have been made worse by low river flows combined with warmer summer temperatures.

Water quality in Riversdale Lagoon was unsuitable for swimming for much of the season and we recommend that it be avoided at all times.

See our bathing water quality pages to find out more about where water quality is suitable for swimming.

What can you do?

• Keep animals, especially cattle, out of rivers and streams.
• Don't put chemicals or any other waste in stormwater drains, rivers or streams.
• Find out about stream care groups in your area and get involved in planting trees and shrubs along waterways. Streamside planting helps stop pollution reaching the water, protects the stream banks from erosion and provides shade so that the water stays cool in the summer.

What is Greater Wellington - The Regional Council doing?

Investigation: investigating types of pollution entering streams and rivers from stormwater drains. When we know what the pollutants are and where they are coming from, we can work with the territorial authorities to reduce or stop them.

Education: running a Take Action for Water programme in primary schools. The programme aims to educate young people about the nature of rivers and streams and how to look after them.

Greater Wellington is developing Take Charge - a pollution prevention programme to improve industrial discharge practices. We also support and work with stream care groups throughout the Region, promoting the restoration of streams and riparian areas.

Riparian management: managing riparian areas to bring about a steady improvement in water quality. We promote streamside retirement and planting where it can provide benefit to stream health. Riparian management trials are underway on the Karori, Kakariki and Enaki streams.

Regulation: controlling the discharge of pollutants into water through the Regional Freshwater Plan.