From November to March we monitor faecal contamination at marine and freshwater (lakes and rivers) sites. We also check for toxic algae (cyanobacteria) at lakes and rivers.
Regular monitoring helps us to assess conditions, trends, and public health risks. Grades follow guidelines from the Ministry for the Environment and the Ministry of Health.
Long-term grades:Each site is given a long-term grade prior to the summer monitoring season for suitability for swimming and recreation, based on the last five years of faecal indicator bacteria sampling. Long-term grades remain in place for the whole summer and are only reassessed after each monitoring season.
Temporary health warnings:Are for sites that were graded as suitable for contact recreation at the start of the monitoring season, but subsequently high levels of faecal indicator bacteria are found in weekly samples. They are issued by National Public Health Service. Temporary health warnings are lifted when samples show the faecal indicator bacteria concentrations are generally suitable for swimming. This may require more than one sample with low faecal bacteria levels indicator for the health warning to be lifted. Find out more about temporary health warnings.
Weekly results vs long-term grades
Because long-term grades are based on the last five years of faecalindicator bacteria sampling, it is possible for sites to have good weekly results while still holding a long-term grade of poor.Long-term grades are reassessed at the end of the current monitoring season and updated annually.
Why long-term grades matter: Water quality can change daily, which is why a long-term assessment of risk is used to grade a site’s overall suitability for swimming. Long-term grades are based on data from the past five monitoring seasons.
Limitations of weekly results: Results can take 2-3 days to be returned after samples are collected, meaning weekly results are not reflective of real-time water quality. Our trial of the predictive water quality tool for Lyttelton and Akaroa harbours is designed to give a more up-to-date view of what’s happening right now based on current climatic factors.
Calculating long-term grades: We use the Ministry of Health guidelines to calculate long-term grades. To work out the risk, we use the past five years of samples (minimum of 15 samples per year).
Coastal sites: For enterococci testing at coastal sites, the guidelines say that if a site has more than 5 per cent of samples (for example, 5 out of 100) which exceed 500 enterococci/100ml (coastal waters) then that site is deemed to have a high overall health risk and is not considered suitable for activities where you come into contact with water.
Rivers and lakes: For E. coli testing in river and lake sites, the guidelines say that if a site has more than 5 per cent of samples (i.e., 5 out of 100) which exceed 550 E. coli/100ml (rivers and lakes) then that site is deemed to have a high overall health risk and is not considered suitable for activities where you come into contact with water.
Predictive water quality model
The new predictive tool gives a clearer, more up-to-date picture of current water quality because it makes hourly predictions and is responsive to changes in weather and other climatic conditions. We anticipate that the model will be ready for use for the summer swimming season.
Why it matters: Without a predictive tool, sites with poor long-term grades are shown as unsuitable for swimming all summer.
Which sites are included?
To improve real-time information, we’re trialling a predictive model at 13 bays in:
Akaroa Harbour (Akaroa Main Beach, Duvauchelle, French Farm, Glen, Takamatua, Tikao, Wainui)
Cass Bay and Governors Bay Sandy Beach:
The model for Cass Bay and Governors Bay Sandy Beach is not yet accurate enough for real-time safety updates and may give false “suitable” results. We’re collecting more data this summer, especially after rain, to improve forecasts. Cass Bay usually has good long-term water quality, while Sandy Beach is graded ‘unsuitable for swimming’ due to ongoing health risks.
How the predictive model works
The predictive water quality model uses more than 11 years of sampling data and real-time conditions to estimate enterococci levels at popular swimming spots across Canterbury.
By predicting concentrations hourly, the model provides a much more accurate picture of current swimming safety than traditional long-term grades or weekly results.
Learn more about how the model predicts water quality, why real-time results matter, and how we ensure accuracy and ongoing improvements:
How the model makes predictions
The predictive tool is a mathematical model that combines:
historical enterococci sampling results (over the past 11 years)
real-time environmental factors such as weather, tides, and site-specific conditions
Using this information, the model estimates current enterococci concentrations in real time. Predictions are displayed as:
Green – suitable for swimming and other water-based activities
Red – not suitable for swimming.
Why real-time water quality predictions matter
Real-time models are valuable because they account for all the historical understanding we have, and factor in real-time conditions that might change enterococci concentrations. This means they’re able to predict what the water quality is likely to be at any given time. The model will continue to be improved after each season as new water quality samples are collected.
Accuracy and ongoing improvements
The model is trained on, and tested against, real data, to predict real-time enterococci concentrations.
Our model meets national and international standards at each of the 13 sites. We will also continue to collect weekly samples (to capture all weather conditions) as well as additional samples during and after wet weather, so that the model can be refined at the end of each season.
During the summer, our scientists will be checking the real-time predictions against weather conditions to ensure that the model is working correctly and make adjustments as needed.
A predictive water quality model requires a large number of samples, and in particular samples during wet weather, to have confidence in the accuracy of its predictions.
Search for your site: Enter the name of your preferred swimming spot.
View the status: Check the current water quality status—green (suitable), amber (caution), or red (unsafe).
Understand the status: Click “Why this status?” for details on the current water quality.
Explore historical data: Use “View as graph” to see water quality trends over the past 5 years.
Check real-time predictions: For Lyttelton and Akaroa bays, view real-time water quality forecasts.
What can I do to improve water quality?
We ask the community to be responsible, tips include:
Scoop up any dog poo and dispose of it in the rubbish. If dog poo is left, rain can wash it into the water or stormwater. Do not let your dog swim in the water when the local council has restrictions in place.
Always use the toilets provided and make sure babies and toddlers use swim nappies.
Dispose of any toilet waste from boats and campervans responsibly.
If you notice any unusual discharges to rivers, lakes or the coast report it through the Snap Send Solve app.
If you live on a property that has an on-site wastewater treatment system:
