Recreational Water Quality
Enjoying a swim at the beach or cooling off in a river are essential parts of a Kiwi summer.
Marlborough generally enjoys comparatively good water quality, but there can be instances when the water contains microorganisms that can cause illness in swimmers.
To assess the risk to water users, council collects weekly samples from the most popular swimming sites. Samples are collected during the warmer months of the year, between November and March and analysed for indicator bacteria.
Once samples have been analysed, the results can be viewed on the LAWA website:
Every three years, results are also summarized in a report containing in-depth analysis of seasonal results and changes over time.
Monitoring Sites
Currently Marlborough District Council monitors nine coastal beaches and ten river swimming spots. Site selection is based on popularity assessed via regular surveys.
Monitoring Results
Samples are analysed for different indicator bacteria depending on the type of waterbody. Coastal samples are analysed for Enterococci, while river samples are analysed for E. coli concentrations.
Enterococci and E. coli concentrations are compared to values in the 2003 Guideline document and assigned health risk modes (Green, Amber and Red).
Go to the 2003 Guideline document
The table below shows the indicator bacteria concentrations for the three risk modes in numbers per 100 millilitres.
Mode | Enterococci (Coastal) | E. coli (Rivers) | Meaning |
|---|---|---|---|
Green | <140 | <260 | Safe for Swimming |
Amber | 140 - 280 | 260 - 550 | Increased Health Risk |
Red | >280 | >550 | Unsafe for Swimming |
High indicator bacteria concentrations are generally observed as a result of rainfall when surface run-off carries material into streams and coastal areas. It is therefore recommended to not swim during rainfall and for at least 24 hours after rainfall. On rare occasions high concentrations are caused by local sources, such as animal droppings, or discarded waste.
Suitability for Contact Recreation Grades
The results from individual samples only provide a snapshot and indicator bacteria concentrations can change quickly, for example as a result of rainfall. This is especially important as there is a delay of at least 24 hours before sample results are known and a gap of one week between samples.
To still provide swimmers with relevant information, sites are assigned grades which indicate the overall suitability for swimming. These are the SFR Grades (Suitability for Contact Recreation Grades). There are five Grades ranging from Very Good to Very Poor.
SFR Grade | Meaning |
|---|---|
Very Good | Considered satisfactory for swimming at all times. |
Good | Satisfactory for swimming most of the time with exceptions following rainfall. |
Fair | Generally satisfactory for swimming. Caution should be taken during periods of high rainfall and swimming avoided if water is discoloured. |
Poor | Swimming should be avoided, particularly by the very young, the very old and those with compromised immunity. |
Very Poor | Generally swimming is not recommended. |
There are two parts to grading a swimming site:
Sanitary Inspection Category (SIC) - the SIC is based on an assessment of the risks from possible sources in the area that can affect the concentration of indicator bacteria and associated waterborne diseases.
Microbial Assessment Category (MAC) - the MAC is calculated using sampling results from the latest five summer seasons.
The National Policy Statement for Freshwater Management 2020 (NPS-FM) also uses the MAC values to assign States, but does not use the SIC. Still the NPS-FM states and SFR Grades are mostly the same.
Go to the National Policy Statement for Freshwater Management 2020 (NPS-FM)
Changes Over Time
Assessment of changes over time (trends) allows us to determine if regional objectives, policies, and rules are working and points us to areas where further investigation and mitigation of sources are required.
Marlborough is fortunate to have quite good water quality. However, this means that indicator bacteria concentrations are often below the detection limits which presents a problem for traditional trend analysis.
An alternative is the use of MAC values to provide an indication of changes over time. The MAC (Microbial Assessment Category) is based on a calculated value that is derived using data from five consecutive summer seasons.
A more detailed analysis of trends can be found in the latest full report:
