State of River Water Quality in Tasman

The Council monitors water quality in, which can be analysed over many years to measure the health of our waterways and surrounding environment.

Based upon an analysis of almost 10 years of sampling data to end of 2009 at 75 sites:

Water Quality for Aquatic Ecosystem Health

  • 44% of sites were in excellent or good condition. These sites included forested headwaters and also the downstream reaches of the District’s large rivers. Sites in this group include: Motueka, Takaka, Aorere, Buller, Matakitaki, Waimea, Wairoa, Wangapeka.
  • 13% of sites were in "fair" condition. These sites had satisfactory water quality most of the time, but breached water quality guidelines on occasion. Average water clarity was lower and concentrations of nutrients and faecal bacteria were higher. These sites included small streams and the downstream end of moderate sized rivers that drain intensively developed areas. Sites in this group include: lower Riwaka, lower Sherry (near Tapawera), Mangles (near Murchison), lower Onekaka (Golden Bay), lower Wai-iti (near Brightwater), Motupiko (upper Motueka catchment), Black Valley (in St Arnaud), and Kaituna (near Collingwood).
  • 33% of sites were in poor condition. These sites had poor water clarity and high concentrations of nutrients and faecal indicator bacteria compared with other sites in the District and often exceeded water quality guidelines. Summer-time dissolved oxygen concentrations were low at times in some of these small streams. All of these sites are on small streams draining low elevation land that has been intensively developed for agriculture, horticulture, or urban usage. Sites in this group include: Motupipi, Watercress and Winter Creeks (near Takaka), Little Sydney and Waiwhero Creeks (near Motueka), Kikiwa (upper Motueka) and Reservoir Creek in Richmond.

Macro-invertebrate communities indicated good ecosystem health at the majority of the sites that were sampled. However, ecosystem health appears to be poor in many of the small lowland streams that drain the intensively developed parts of the District (eg, Motupipi River, Watercress Creek, lower Reservoir Creek, Waiwhero, Little Sydney). These sites were also identified as having poor water quality.

Biological growths on the beds of waterways (including algae) also indicate good ecosystem health at the majority of monitoring sites. However, once again, the small lowland streams draining intensively developed land often had excessive accumulations of nuisance algae.

Water Quality for Swimming

Monitored swimming holes have water quality that is safe to swim in 98% of the time unless the river is affected by rain. Usually it takes less than 24 hours after the rain stops for the water quality to become safe again.

  • Only two sites in the programme were considered either too slimy or levels of disease-causing organisms too high
  • 19% of sites were considered "fair" These sites had satisfactory water quality most of the time, but breached water quality guidelines on occasion

The effects of land use on water quality are widely recognised and the results of this analysis are consistent with water quality patterns across New Zealand.
The State of New Zealand's Rivers

Trends in River Water Quality

Trends in water quality were determined at 13 sites, 9 of these showing an improvement in water quality. 

Confidence with trend analysis was strongest for the three National River Water Quality Network sites: Motueka at Gorge (upper reference site), Motueka at Woodstock (lower site), Buller at Longford (mid catchment near Murchison). This is because of the amount of data available for these sites; sampling has been conducted at these sites monthly since 1989. Concentrations of ammonium nitrogen declined at all three sites over the course of the data record, whereas concentrations of total nitrogen and nitrate increased at the mid Buller and lower Motueka sites. Water clarity also tended to increase at all three sites, including the Gorge site, which is upstream of any human land use, over the course of the data record. The fact that these changes were consistent among all three sites suggests that this trend is related to climatic changes, rather than changes in land management. However, nitrate nitrogen concentrations and conductivity increased significantly at the Motueka River at Woodstock site over the course of the data record, but not at the other sites, suggesting that these changes may be related to changes in land use within the Motueka Catchment since monitoring began in 1989. Total nitrogen also increased at the Buller site. Macro-invertebrate condition (MCI and QMCI) is getting worse at Woodstock and Longford. 

Trends detected in the SOE sites show reducing dissolved nitrogen in the Aorere at Devils Boots, reduced levels of disease-causing organisms in the Wairoa River and improved water clarity at Takaka at Harwoods (upper site). However, increasing nitrate levels were found in the Sherry River.

River Water Quality Investigations in Specific Catchments

Water Quality Glossary

What Monitored Indictors Tell Us About Water Quality

Types of Rivers in Tasman