How SFR Grades Are Assigned

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How SFR Grades Are Assigned

Council uses the 'BatheWatch' software provided by the Ministry for the Environment to assign SFR Grades.

See the Ministry for the Environment BatheWatch user guide

There are two components to the assignment:

SIC (Sanitary Inspection Category)

The SIC is based on the assessment of potential sources of faecal contamination that could have an impact on the water quality of a site. The key steps are:

  1. Identifying potential pollution sources. Pollution sources include pastoral land use, sewage storage and treatment systems, large numbers of aquatic birds and feral animals.
  2. Determining the likelihood of each source affecting the site. For each pollution source the potential of causing high indicator bacteria concentrations at the site is considered.
  3. Assign a SIC. The SICs are categorized as very low, low, moderate, high or very high.

MAC (Microbiological Assessment Category)

The MAC is based on the actual indicator bacteria concentrations that have been measured over five summer season at a site. The statistic used for the calculation of the MAC is the upper 95th percentile.

Find out more about indicator bacteria

Find out more about MAC calculation

The table below shows the MACs and the associated values for the two indicator bacteria:

MAC
(microbiological Assessment Category)
Coastal
Enterococci/100 mL*
Freshwater
E.coli/100 mL*
A <41 <131
B 41 - 200 131 - 260
C 201 - 500 261 - 550
D >500 >550

* Upper 95th percentile (95%ile) of routine sampling over five consecutive summers.

Assignment of the SFR Grade

Once the SIC and MAC for a site have been determined an SFR Grade can be assigned (see table below).

SFR Grade (Suitability for Contact Recreation Grade) MAC (Microbiological Assessment Category
A B C D
SIC (Sanitary Inspection Category) Very Low Very Good Very Good * *
Low Very Good Good Fair *
Moderate * Good Fair Poor
High * * Poor Very Poor
Very High * * * Very Poor

*Unexpected result (further investigation is necessary).