What Specific Indicators Tell Us About Water Quality

Indicators are parameters that are good at describing the state or condition (of the river). This page describes some of the most important indicators.

Faecal Bacteria

High levels of disease-causing organisms in our waterways are one of the district's most widespread water quality issues. The concentrations of E.coli (the indicator bacteria used) can be 10-100 times higher in flood conditions. In some situations these concentrations are affecting shellfish harvesting for several kilometers off the river mouth. The source of this contaminant has been identified as mainly from cattle in the Aorere River, and both cattle and humans in Murchison Creek and Tasman Valley Stream. Levels in native or exotic forest are very low and always swimmable.

Water Clarity

Tasman has many rivers that have exceptional water clarity. Waikoropupu River (flowing from Pupu springs) takes top spot at 62m. The only other place in the world with higher clarity is under ice in Antarctic lakes. Upper Matakitaki, Waingaro and upper Motueka have all had water clarity readings over 20m, which puts them amongst the highest in New Zealand.

Nutrients

Nutrient concentrations are only an issue in a few catchments in Tasman, partly due to many streams having significant dilution from clean headwater streams. The Motupipi River is one catchment that has particularly high nitrogen and phosphorus and is intensively farmed. Estimates of nitrogen loads (total quantity) for all waterways are available. The information is produced from a model using data collected by Council and the national river water quality network.

Water Temperature

Continuous water temperature records from over 40 sites throughout the district show that well-shaded headwater streams never exceeded the temperature criteria for protecting ecosystem health during the summer. However, the water temperature criterion was regularly exceeded during summer at sites on small unshaded streams draining developed land (eg, Reservoir, Waiwhero, Little Sydney, Kikiwa, Sherry, Tadmor, Tasman Valley). The cold rivers such as the Baton, Pearse and Graham on Motueka's west bank cool the Motueka River to just within the criterion most of the time.