E.coli Management

E. coli bacteria are found in the gut of animals including humans. They enter rivers directly from the faeces of wild and domesticated animals standing or swimming in water, or indirectly from animals on land, washed into rivers during rain events.

E. coli bacteria are found in the gut of animals including humans. They enter rivers directly from the faeces of wild and domesticated animals standing or swimming in water, or indirectly from animals on land, washed into rivers during rain events.

Council and Landcare trust NZ have worked together to produce useful resources for landowners on riparian planting (2.1MB PDF) and managing pollutants (1.9MB PDF)

E.coli bacteria can persist in the environment for weeks, if not indefinitely in soils and sediment, which needs to be considered when assessing the source of the bacteria.

Maitai river swimming holes

Whilst strains of E. coli bacteria are potentially harmful to humans, E. coli is routinely used to indicate the presence of other harmful viruses and pathogens that can occur with high levels of bacteria.

In 2018, Council undertook E.coli monitoring in the Wakapuaka catchment. You can find the results of this monitoring programme here.

 Lab Testing

Lab testing identifies E. coli markers for general bacteria and ruminants, and specific markers for human, sheep, cow, birds and human faecal sources. Each marker is strongly associated with the source tested for, however, the relative contribution of each marker in a water sample cannot be compared. 

 E.coli source tracking

The percentage value or ‘consistent match’ of the E. coli marker is used to identify whether the faeces has a high consistent match (50-100%) with a specific animal marker.  Lower percentage matches (10-50%) may indicate aged faeces with declining markers or from other sources of pollution.

E.coli sources

All animals on land within the catchment, whether farmed or wild, will contribute to faecal matter getting into waterways.

Cattle standing in streams or wet areas will deposit faeces directly into waterways while doing so. This can be managed by excluding stock from streams by fencing along streams to prevent access.. 

Animals grazing on land which is adjacent to water, such as farmed sheep, cattle and horses, will deposit faeces on the land.  The bacteria from the animal faeces is washed into the streams during heavy rain. 

Managing E.coli

The most effective approach to preventing stream pollution with E.coli is to fence and plant stream margins. This both excludes stock from directly polluting the water, and reduces E.coli contamination from runoff from grazed land.

Fencing the streamside will keep the livestock from depositing faeces directly in the river and also reduce stream bank erosion and stream bed compaction from livestock trampling.

Leaving the grass on riverbanks long, and planting the riparian margins within the fence lines will assist stabilizing the bank from erosion and reduce direct surface runoff and bacteria entering the stream.

Other E.coli management approaches include small wetland filter systems at those low points where runoff will enter the river or streams, and planting of ephemeral streams which don’t hold water all year, but will run during rain events and wash faecal matter into the river.

Appropriately maintaining septic tanks is also important in rural residential areas.