Faecal indicators

Escherichia coli (E. coli ) is an indicator of pathogens associated with faecal contamination of water bodies. These may have an impact on native and domesticated animals, as well as on human health. The primary sources of faecal contamination in New Zealand are waste from humans and farmed animals such as sheep and cows. Other sources include dense bird populations.

If you want to find out more about faecal indicators, have a look at the factsheet.

Current national state

The map below shows the estimated concentration of E. coli in waterways across New Zealand. Higher concentrations are generally found in rivers and streams in Auckland and on the lowland 'plain' regions such as the Waikato and Hauraki Plains, Manawatu Plains and the low-lying areas of Southland. Some point sources such as urban wastewater discharges and farm effluent treatment ponds are not identified well in the model, and data from monitoring sites might show higher E. coli levels in these places.

National E. coli concentrations

Site Data

This map provides the site locations and value of the monitoring data, which was used to set up the model.

Modelled Data

The map illustrates the modelled condition across the country from highest to lowest. The dots indicate the site location and value of the monitoring data, which was used to set up the model.

Comparison Data

The map shows a comparison between modelled concentrations and actual monitoring site data. Symbols show where the site data was substantially (50%) better than the model predicts, or substantially (50%) worse.

E. coli concentrations for different land-cover classes

The effect of land cover on predicted E. coli concentrations is substantial. Stream reaches in urban influenced catchments have much higher median E. coli concentrations, compared to all other land cover types, and nearly 100 times that of predominately indigenous vegetation.  This may be associated with wastewater and sewerage infrastructure. River reaches in catchments dominated by pasture and exotic forest are estimated to have median concentrations 40 times and ten times higher, respectively than streams running through predominantly indigenous land cover.

The source of the high concentrations in pasture is likely to be grazing animals and possibly septic systems. In contrast, it is unclear where the relatively high E. coli concentrations in sites with exotic forest come from, but is possibly the influence of other activities in the catchment.

National E. coli concentrations across four different land cover classes

E. coli boxplot

What is this type of graph?

Recent national trends

Recent national trends are calculated using data from a 10-year period to be confident that any detected trend is the result of a genuine pattern, rather than random and variable events such as heavy rainfall.

Note that the representativeness of the monitoring network which these trends are based on is limited. This means that the data may not represent wider trends across the whole of New Zealand as more sites have been sampled in more problematic areas such as lowlands, cities and intensive land uses. This gives us a useful picture of what is happening in the areas where people have the most impact on the environment, however, not so much of an idea what is happening in less extensively used areas such as native forests.

Our analysis showed no significant trend at the majority of monitoring sites across all four land-use types. Overall, however, more sites improved (13%), than worsened (8%). A number of monitoring sites in urban areas improved (23%), but these rivers represent less than 1% of the New Zealand total (indicated graphically by the small size of the column):

Percentage of monitoring sites with significant trends in observations of E. coli concentrations across four land-cover classes

E.coli concentrations across land cover classes

What is this type of graph?

See also:

– Nutrients: Total phosphorus, dissolved reactive phosphorus and nitrate-nitrogen
Benthic macroinvertebrates