During the swimming season (November to March), regional, district and city councils and public health agencies assess the health risks from faecal contamination at swimming spots. LAWA displays the results of recreational monitoring at popular rivers, lakes and beaches, providing both an Overall Recreation Risk as well as the most recent monitoring results.
Why can water cause illness?
When contaminated by human or animal faeces water can contain disease-causing bacteria, viruses and protozoa (such as salmonella, campylobacter or giardia). These organisms can pose a health risk in water that is used for recreational activities such as swimming. The most common illness is gastroenteritis but respiratory illness and ear and skin infections may also occur.
How is the risk from faecal contamination assessed at swimming spots?
The quality of water for swimming is determined by measuring ‘faecal indicator bacteria’ (E. coli in rivers and lakes) which indicate the levels of disease causing organisms in the water.in coastal waters and
What does the Overall Recreation Risk mean?
The Overall Recreation Risk is a guide to give a general picture of water quality at a site. Updated annually, it is calculated from bacteria data (E. coli for freshwater or enterococci for coastal waters) collected over the last three years. The Overall Recreation Risk indicator provides a measure of health risk at a site, with the highest risk category set at a threshold of 5% risk of infection for fresh water and 10% for coastal water. However, a site with 'Caution' can be suitable for swimming some of the time.
What do the risk categories mean?
The Overall Recreation Risk uses four categories to show the risk of gastrointestinal illness from primary contact with the water:
Description of risk
Description of risk
|Overall recreation risk||Enterococci/100 ml (number of enterococci per hundred millilitres)||E. coli/100 ml (number of E.coli per hundred millilitres) |
|Very low risk||Equal to or less than 40||People are exposed to a very low risk of infection (up to 1%) from contact with the water||Equal to or less than 130||People are exposed to a very low risk of infection (up to 0.1%) from contact with the water|
|Low risk||41-200||People are exposed to a low risk of infection (between 1 and 5%) from contact with the water||131-260||People are exposed to a low risk of infection (between 0.1 and 1%) from contact with the water|
|Moderate risk||201-500||People are exposed to a moderate risk of infection (between 5 and 10%) from contact with the water. This is the minimum acceptable state||261-540||People are exposed to a moderate risk of infection (between 1 and 5%) from contact with the water. This is the minimum acceptable state|
|Caution||More than 500||People are exposed to a high risk of infection (greater than 10%) from contact with the water||More than 540||People are exposed to a high risk of infection (greater than 5%) from contact with the water|
How is the Overall Recreation Risk calculated?
The Overall Recreation Risk presented on LAWA is based on the 95th percentile of sample results from the last three years. The use of a 95th percentile statistic (and the associated risk categories) aligns with the Microbiological Assessment Category (MAC) outlined in the 2003 MFE/MOH Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas. A site must have at least 30 water sample results (with at least 10 in each year) in order for an Overall Recreation Risk to be calculated. LAWA has chosen to use three years of sampling so that weather conditions over several summers are taken into account.
Wet weather influences bacteria counts and hence the 95th percentile is influenced by weather conditions. For example, a wet summer is likely to lead to a higher risk category being assigned to a site. Some councils factor the influence of rainfall into their monitoring results by limiting sampling to dry weather conditions when people are more likely to be swimming. Other councils remove rainfall-related bacteria results prior to calculating 95th percentile. Because there is not currently a standardised national method for adjusting rainfall-related sample data, no adjustments have been made to any bacteria data presented on LAWA (All sample results regardless of weather conditions, have been used in the risk calculations).
What is the summer season monitoring?
While the Overall Recreation Risk gives a general guide to the water’s suitability for swimming, most councils also report weekly water sampling to inform the public of any immediate risk from contact with the water. The weekly water sample is a snapshot in time. It’s important to remember that even spots with low risk can be unsuitable to swim in at times. We recommend that you avoid swimming up to 48 hours after heavy rainfall as urban or agricultural run-off may affect bathing water quality at these times.
What do the summer season icons mean?
The 2003 MFE/MOH Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas specify acceptable levels of bacteria and help councils determine when action needs to be taken to increase monitoring or issue health warnings.
LAWA uses the symbols below to show the result of weekly recreational monitoring :
|Acceptable – Continue routine monitoring||Acceptable – Alert. Increase monitoring and investigate source||Unacceptable – Action. Immediate re-sample, public warning issued if required, increased monitoring and investigate source|
# of indicator bacteria
|Beach: Enterococci/100ml||Equal to or less than 140 Enterococci/100ml||More than 140 Enterococci/100ml||More than 280 Enterococci/100ml|
|River/Lake: E. coli/100ml||Equal to or less than 260 E. coli/100ml||More than 260 E. coli/100ml||More than 550 E. coli/100ml|
The weekly sample doesn’t exceed the ‘alert’ indicator bacteria level specified in the guidelines, and the beach’s water quality doesn’t present an immediate health risk to those in direct contact with it. Monitoring continues on a regular (usually weekly) basis.
If a sample exceeds the ‘alert’ indicator bacteria level specified in the guidelines, the water still meets an acceptable standard for swimming but an alert is triggered for councils to undertake further investigation.
Under alert mode monitoring should increase to daily sampling and councils should work to identify the sources of contamination and management options.
If a sample exceeds the ‘action’ indicator bacteria level, the water is considered unacceptable or unsafe for swimming. Under the action mode, the local authority and health authorities warn the public that the area is unsuitable for recreation and arrange for the local authority to erect signs at the area warning the public of a health danger.
Note that under the MFE/MOH 2003 guidelines, health warnings for coastal waters are only issued after two consecutive samples (within 24 hours) exceed the ‘action’ level.
How can the weekly monitoring result be acceptable when the Overall Recreation Risk is 'Caution'?
Sometimes a site can have an Overall Recreation Risk of 'Caution' but the most recent samples indicate that that water quality is within the acceptable range for swimming. This is because the Overall Recreation Risk is calculated using results over three years and, particularly for rivers, may have been impacted by a wet season causing high flows and bacteria contamination from run-off.
If the most recent sample result is within the acceptable limits and there hasn’t been heavy rainfall since the sample date, it is likely that the water quality will still be safe for swimming. You can also click on the summer season monitoring to view the results of previous weeks’ monitoring. This will give you an idea of what the water quality has been like in recent weeks.
What other risks are not accounted for?
Swimming at your favourite beach, river or water hole presents additional safety risks. At some river and lake sites the weekly testing does not measure the presence of cyanobacteria (a blue-green algae that can be toxic) and other toxic algal species which may be harmful if ingested, stinging jellyfish, high water flow and strong tidal currents. Furthermore there are times when other contaminants that are not monitored can make bathing waters unsuitable for swimming. Members of the public must be aware of such risks when swimming.
What is the impact of rainfall?
Water quality at many river and beach swimming spots is affected in wet weather as a result of urban or rural runoff. In urban areas rainwater collected from roofs, roads, car parks and other surfaces is piped directly into rivers, streams and the coast. During its travels, this storm water picks up sediment, rubbish, contaminants, and dog and bird droppings. Sewer overflows can also occur in urban areas during wet weather. In rural areas, excess rainwater flows over the land and into nearby streams and rivers, picking up manure and other contaminants along the way. At some river, lake and coastal sites, heavy rain and wind can churn up sediments from the bottom of the waterway or sea, releasing pathogens in the sediments back into the water.
The roles and responsibilities of agencies
Monitoring of recreational water quality involves multiple agencies: regional councils, district and city councils and health agencies. The roles and responsibilities can vary in each region but most follow those recommended by the 2003 MFE/MOH Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas.
The Regional/Unitary Council is responsible for implementing a monitoring programme. This includes:
- Weekly sampling at popular swimming sites
- Investigations of sources of contamination
- Informing the Medical Officer of Health (Community and Public Health) and the local district or city council if alert or action levels are reached
- Collating information for annual reporting and for grading of sites.
The Medical Officer of Health at Community and Public Health is responsible for:
- Reviewing the effectiveness of the monitoring and reporting strategy
- Ensuring the territorial authority is informed
- Ensuring the territorial authority informs the public of any health risks.
The district or city council is responsible for:
- Informing the public when the action level is exceeded
- Assisting with identifying sources of contamination
- Implementing steps to abate or remove any sources of contamination.
Find out more
- For more information about recreational water monitoring in a specific region contact your regional council.
- You can also find out more about recreational water quality monitoring from the 2003 MFE/MOH Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas
- Cawthron Institute - Cawthron Institute scientist Dr Susie Wood is a world expert in cyanobacteria (also known as toxic or blue-green algae). In this video Dr Wood talks about toxic algae in New Zealand rivers and what we need to look out for to keep ourselves safe. See more at: http://www.cawthron.org.nz/coastal-freshwater/news/2016/toxic-algae-and-what-you-need-look-out/#sthash.RzfAm78J.dpuf