Factsheet: Coastal and freshwater recreation monitoring

Why can water cause illness?

When contaminated by human or animal faeces (‘poo’), water can contain disease-causing bacteria, viruses and protozoa (such as salmonella, campylobacter or giardia). These organisms can present 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.

The quality of water for swimming is determined by measuring ‘faecal indicator bacteria’ (enterococci in coastal waters and E. coli  in rivers and lakes) which indicate the levels of disease causing organisms in the water.   See this factsheet on faecal indicator bacteria to find out more.

Toxic algae (cyanobacteria) can become a problem in some lakes and rivers when there are large amounts present (known as toxic algal blooms).  Some cyanobacterial species are known to produce poison or toxins, but they are not toxic all the time.  See this factsheet on toxic algae for more information.

 

What does the summer recreational season monitoring information tell us?

For most sites, LAWA shows the recent water quality result, and the results from the last five years of sampling over the recreational bathing season which is used to determine the long-term grade.  Both types of information can be used as a guide for you to decide where it is suitable to swim. 

See 'what do the swim icons mean?' factsheet for more.

 

Weekly sampling & predicted water quality results

Faecal indicator bacteria

Most councils monitor the water quality weekly over the summer months to inform the public of any immediate risk from contact with the water.  The weekly sample result is a recent snapshot in time - it tells you what the water quality was like at the time of sampling.  It’s important to remember that water quality can change over time, especially after rain.  That is why we recommend that even for sites with generally good water quality, that you avoid swimming 2 - 3 days after heavy rainfall as urban or agricultural run-off can affect bathing water quality.

In the Auckland and Wellington regions, and for many Northland region swim sites, water quality is predicted using models.  The predicted water quality results are regularly updated to give a 'real-time' result.  The modelling takes environmental conditions (e.g. rain, tides, storm water overflows for Auckland sites, and rain for Wellington sites) into account when determining the predicted water quality risk status for sites in these regions.

National Guidelines for faecal indicator bacteria (2003 MFE/MOH Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas and the National Policy Statement for Freshwater Management (2020) for freshwater sites) provide trigger levels that allow councils to assess individual monitoring results and determine when management intervention is required. The trigger levels and corresponding management responses are shown in the table below.

When water quality falls in the ‘surveillance’ category this indicates that the risk of illness from swimming is low. If water quality falls into the ‘alert’ category, this indicates an increased risk of illness from swimming, but still within an acceptable range. However, if water quality enters the ‘action’ category, then the water poses an unacceptable health risk from swimming.

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.  

 

Toxic algae 

The risk to people and animals from toxic algae is determined by measuring the proportion of the river bed covered by cyanobacteria as well as the amount of cyanobacteria mats washed up on the river’s edge, or the amount of cyanobacteria suspended in the water column in lakes or slow flowing waterways.

Results are compared to national guidelines for toxic algae (New Zealand guidelines for cyanobacteria in recreational fresh water: interim guidelines) which provide trigger levels that allow councils to assess individual monitoring results and determine when management intervention is required. The trigger levels and corresponding management responses are shown in the table below.

Not all recreational sites are monitored for toxic algae.  As it can be harmful, even in small amounts, we recommend you know what it looks like, and avoid contact when you see it.

 

Long-term grade

The long-term grade is a precautionary guide to the general water quality by determining whether a site overall is excellent, good, fair or poor for swimming over the recreational bathing season. Updated annually, it is calculated from bacteria data (E. coli for freshwater or enterococci for coastal waters).  The long-term grade is risk based and doesn't necessarily reflect the conditions on a particular day. 

The long-term grade aligns with the Microbiological Assessment Category (MAC) in the 2003 MFE/MOH Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas for coastal sites, and the attribute bands (table 22) in the National Policy Statement for Freshwater Management (2020) for freshwater sites.

 

What does this mean in practice?

Sites categorised excellent, good, and fair have water quality suitable for swimming more often than the sites graded poor over the past five summers. The poor category represents a wide range of water quality results, from sites that may have exceeded the swim guidelines once or twice per season, to sites with repeated, ongoing exceedances. Many popular swim spots are known to exceed the guidelines following adverse weather conditions yet outside of this have suitable water quality for swimming. That’s why we advise swimmers to avoid the water for 2 – 3 days following heavy rain, regardless of the most recent monitoring result or the long-term grade. When deciding where to swim, a ‘poor’ grade can be viewed as a signal to look closer at the data under ‘why this status?’ on the site page to understand the performance of that swim spot over time.

How is the long-term grade calculated?

The long-term grade presented on LAWA is based on the hazen 95th percentile of sample results from the last five recreational bathing seasons.  In simple terms, if a site was calculated to have a 95th percentile of 200, then this means that 95 out of 100 times that this site was monitored, that the results were at or below  200 E. coli / 100 mL for freshwater sites, or 200 enterococci/100 mL for coastal beaches. Notes on the analysis:

• Samples included in the analyses were taken from the recreational bathing season (last week in October through to the end of March) each year.
• Recreational bathing season data over the last five years were used so that weather conditions over several summers are represented.   
• At least 50 sample results over the last five recreational bathing seasons (2019/20 - 2023/24) was required, and sites must be part of a recent monitoring programme.  Sites that haven't been regularly monitored in either of the last two bathing seasons (2022/23 and/or 2023/24) were excluded from the analyses, even if they had at least 50 data points.
• LAWA used routine sampling results.  Data which were from follow up samples, taken as a response to elevated results, have been excluded from the analyses where councils can provide metadata to LAWA that identify these re-samples.
• Some estuarine sites are monitored for both enterococci and E. coli.  In these instances LAWA applies a precautionary approach by assigning the worst result from the two bacterial indicators for the long-term grade. 
• Note that the long-term grade doesn't include toxic algal data, or other factors (e.g. swift river or tidal flows) that might make a site unsuitable for swimming.

 

Wet weather can cause bacteria to flow from land into rivers and streams.  Therefore wet weather can influence bacteria counts, and lead to higher risks being assigned after wet summers.  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 (i.e. all routine sample results regardless of weather conditions, have been used in the long-term risk grade calculations).   

FAQ

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.

How can the weekly monitoring result be 'suitable for swimming' when the long-term grade is 'poor'?

A 'poor' long-term grade means that there is an elevated risk of illness compared to sites with better grades. A site can have an long-term grade that is 'poor', but the most recent samples indicate that that water quality is within the acceptable range for swimming. This is because the long-term grade is calculated using results over five years and, particularly for rivers, may have been impacted by heavy rain causing high flows and bacteria contamination from run-off.

For sites graded 'poor', it is best to review the historical data to see whether the monitoring results frequently exceed guidelines.  If they do, it is best to choose another place to swim.  Some sites may be graded 'poor' because while the majority of the test results passed the guidelines, there were some instances of the water quality exceeding the guidelines.  Generally if the most recent results show the water quality met the swimming guidelines, the water looks clean and clear, there hasn't been recent heavy rainfall since the last sample date, and there are no pollution sources nearby, it is likely that the water quality will still be suitable for swimming.  If you have further questions about a site, we recommend contacting the council who undertakes the monitoring for more information. 

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 toxic algae (cyanobacteria) which may be harmful if ingested (young children who put things in their mouth are most at risk), stinging jellyfish, high water flow, or strong tidal currents etc. Furthermore there are times when other contaminants that are not monitored can make bathing waters unsuitable for swimming.  Please be aware of such risks when swimming.

 

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 councils and unitary authorities are 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.

In addition, under the National Policy Statement for Freshwater Management (2020), regional councils and unitary authorities are also required to take practicable steps to notify the public when designated freshwater primary contact sites exceed 540 E. coli per 100 mL during the bathing season. 

 

Find out more

• For more information about recreational water monitoring in a region contact the local regional or unitary council.
• Factsheet on faecal indicator bacteria
• Factsheet on toxic algae
• National Guidelines for recreational water quality monitoring from the 2003 MFE/MOH Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas
  
• National Guidelines for toxic algae monitoring - New Zealand guidelines for cyanobacteria in recreational fresh water: interim guidelines
• National Policy Statement for Freshwater Management 2020