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Fresh water River water quality
Bacteria levels in rivers and lakes
To report on bacteria levels in rivers, streams and lakes, Escherichia coli (E. coli) is measured. E. coli indicate the presence of faecal material in fresh water which, in turn, indicates the presence of disease-causing micro-organisms.
Current situation
About 300 sites on rivers and lakes throughout New Zealand are regularly monitored for recreational water quality over the summer by regional and district councils.
Over the 2007-2008 and 2008-2009 summers, 58 per cent of the 300 monitored freshwater swimming spots had water quality that met the guidelines for contact recreation almost all of the time (ie, at least 95 per cent of the samples taken at these sites had safe E. coli levels).
Only 8 per cent of the sites breached the guidelines regularly (ie, more than 25 per cent of the samples taken from these sites were non-compliant), indicating that these sites often have poor water quality and are unsuitable for swimming.
Bacteria levels are often highest after rainfall when faecal matter is carried from the land into waterways. Examples of common sources of bacteria include effluent run-off from farmland, human wastewater discharges, stormwater outfalls and domestic and wild animal waste. The level of bacteria in rivers can also be affected by natural factors. More on land use influences on bacteria levels in rivers and lakes.
The sites in the national network have been ranked based on nutrient levels, water clarity, bacterial levels, macroinvertebrates and periphyton. The results are presented in river water quality league tables.
Long-term trends
National scale data for E. coli levels at swimming spots has been collated for six summers, from 2003/2004 to 2008/2009. These results suggest that recreational water quality at monitored freshwater sites has been relatively stable at a national-scale, over the last six years. The number of sites with samples that met the guidelines for contact recreation on at least 95% of sampling occasions has fluctuated between 41 and 60 per cent during that period.
E. coli has only been routinely monitored at sites in the National River Water Quality Network since 2005. Again, it is too early to make interpretations about trends from this data but this should be possible in the near future once five years of data has been collected (from 2010 onwards).
E. coli bacteria levels at the 77 national network sites, 2005 - 2007
Note: Hazen method used to calculate 5th and 95th percentiles.
Data source: compiled by the Ministry for the Environment using data collected by the National Institute of Water and Atmospheric Research (NIWA).
Data source: compiled by the Ministry for the Environment using data collected by the National Institute of Water and Atmospheric Research (NIWA).
Read table of data of this graph
What can you do?
- Fence off rivers, lakes and wetlands to help protect our waterways. Planting native vegetation or other plants enhances water quality by filtering sediment, faecal bacteria and nutrients from surface water run-off.
- Farmer? Prevent stock from entering waterways.
- For more advice on stream and wetland protection contact your local or regional council or the New Zealand Landcare Trust.
- Follow urban design and industry best practice guidelines to reduce contaminants getting into waterways.
This information has come from the latest state of the environment report Environment New Zealand 2007.
This data comes from the National River Water Quality Network which is operated by NIWA with funding from the Foundation for Research, Science and Technology.
You can access the national network data for 2007, as well as more site information, in this spreadsheet.
Return to main river water quality page.
Last updated: 10 August 2009
