Waipoua River 20130219.pdf - Northland Regional Council

and short-lived. However, there is the potential for more serious diseases, such as hepatitisA, giardiasis, cryptosporidiosis, campylobacteriosis, and salmonella (MfE 2003).It is difficult to measure the level of faecal pathogens in water. Instead, like other agencies,Northland Regional Council measures the levels of indicator micro-organisms in accordancewith the national microbiological water quality guidelines published by the Ministry for theEnvironment and the Ministry of Health (2003). The Recreational Guidelines usebacteriological indicators associated with the gut of warm-blooded animals to assess the riskof faecal contamination and therefore the potential presence of harmful pathogens.Compliance with the guidelines should ensure that people using water for contact recreationare not exposed to significant health risks. The bacteriological indicator used for freshwateris Escherichia coli (E. coli).The Recreational Guidelines work with a defined ‘tolerable risk’ rather than no risk at all. Formost healthy people coming into contact with water within the guideline value will pose aminimal level of health risk. However, the same water may still pose a greater health risk tohigh-risk user groups such as the very young, the elderly, and those with impaired immunesystems (MfE 2003). Health risks associated with levels of bacteriological indicators arediscussed in further detail in the following sections.In addition, while it is correct to infer that water exceeding the guideline values pose anunacceptable health risk, the converse is not necessarily true. This is because wastewatereffluent may be treated to a level where the indicator bacteria concentrations are very low,but pathogens such as viruses and protozoa may still be present at substantialconcentrations.3.3.1 Contact recreationFor contact recreation the Recreational Guidelines are summarised in Table 9 below. Theyare based on keeping sickness risks associated with recreational water use to less than 2percent (i.e. ≤19 people in 1,000).When levels of E. coli are within the surveillance (green) category, the risk of sickness fromswimming is acceptable, ie, sickness risks are below 19 per 1,000 swimming events (MfE2003). If levels fall into the alert category, there is an increased risk of illness fromswimming, but still within an acceptable range. However, if levels enter the action category(>550 E. coli per 100 mL) then the water poses an unacceptable health risk from swimming.At this point, if the high levels persist, warning signs are erected and the communityinformed that it is “unsafe” to swim at this location.Table 9 Surveillance, alert, and action levels for freshwaterStatus E. coli per 100mL Management actionSurveillance (Green) < 260 Routine monitoring (i.e. weekly)Alert (Amber) 260 – 550 Increased monitoring (i.e. daily), investigation of sourceand risk assessmentAction (Red) > 550 Closure, public warnings, increased monitoring (i.e. daily)and investigation of source30