These must be carefully monitored to ensure they do not pose a threat to health or the environment.
Bacteria biodegrade rapidly in sunlight and saltwater.
In untreated wastewater arriving at the Christchurch wastewater treatment plant the levels are many million faecal coliforms per 100 ml. Tidal flow, dilution and sunlight rapidly reduce the level after discharge. The present treatment plant upgrade will further reduce this level. Additional proposed treatment measures would reduce it yet again. Birds in the ponds and material in the Heathcote and Avon rivers also contribute to an underlying level of faecal coliforms in the Estuary which is independent of the discharged treated wastewater.