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) (2.1MB PDF) and managing pollutants (1.9MB PDF) (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.
Monitoring water quality over the last ten years at Hira and Paremata Reserve swimming holes and throughout the Wakapuaka catchment shows that E. coli bacteria levels can regularly occur at high levels deemed unsafe for contact recreation and stock drinking water. Read the report here
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.
An effective approach to preventing stream pollution with E.coli is to fence and plant stream margins.
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.