National targets for improving water quality for swimming
In 2017 the Government set a national target of making 90 per cent of New Zealand’s large rivers and lakes swimmable by 2040. It set an interim target of 80 per cent swimmable by 2030.
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The National Policy Statement for Freshwater Management (Freshwater NPS) directs regional councils to work towards these targets and report on progress.
The Freshwater NPS is the Government's main direction to regional councils about how to manage freshwater.
Regional councils are required to develop regional targets to contribute to the national target. In March 2018 they made their draft regional targets publicly available. They will make their final regional targets public by the end of 2018.
Every regional council will also need to report regularly on the improvements being made. That means everyone will have access to information about which rivers and lakes are improving, and by how much.
Regional councils are required to improve water quality in terms of its suitability for human health in all freshwater management units, not just the rivers and lakes that count towards the target. Freshwater management units cover all freshwater in their region.
Councils must monitor all freshwater management units (at representative sites) to check progress towards achieving their targets. This is known as ‘grading monitoring’ and must be done monthly. Grading monitoring uses a minimum of 60 samples over a maximum of five years. It will tell you whether water quality is improving over time. If water quality is not improving in terms of E. coli and cyanobacteria, the council may need to make changes to the way it is managing water.
In places and during the months people swim (or other primary contact recreation), councils must monitor E. coli levels weekly. This is called ‘surveillance monitoring’. Councils are now required to investigate sources of microbiological contamination if E. coli levels reach levels where the risk to human health starts to jump (260 E. coli per 100ml), and inform the public if levels get too high (over 540 E. coli per 100ml). These requirements are in line with the “Action” and “Alert” modes in the 2003 Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas.
The national targets are based on five categories, where the best three (blue, green and yellow) are suitable for swimming, and the worst two (orange and red) aren’t.
The aim of the national target is to:
- increase the proportion of rivers and lakes that are suitable for swimming more often
- decrease the proportion of time that rivers and lakes are unsuitable for swimming
- get improvements across the board.
The targets mean that water quality will have to improve from what it is now and, over time, rivers and lakes will be suitable for swimming more often.
To get the most up-to-date information about the state of any river or lake, check out the LAWA website or the regional council’s website – see Council maps and websites.
There are a whole lot of factors that can affect whether a water body is suitable for swimming, but we’ve focused on the two that we consider are the best indicators of potential health risks.
In rivers this is the amount of E. coli in the water as measured over time, while in lakes it’s also based on the amount of cyanobacteria (toxic algae).
Rivers
The table below shows the categories and the attribute states in the National Policy Statement for Freshwater Management and the metrics that define them.
There are a series of tests involved in establishing the categories (attribute states) for rivers from Blue to Red. In New Zealand, there is a high correlation between the tests. If you meet one, it is highly likely that all tests will be met.
Table 1. The E. coli swimming categories (attribute states) in detail
| Category | Percentage of exceedances over 540 E.coli per 100ml | Percentage of samples above 260 E.coli per 100ml | Median: E.coli per 100ml | 95th percentile: E.coli per 100ml | Narrative risk descriptor |
|---|---|---|---|---|---|
| What it means | How often the river exceeds the acceptable threshold for swimming | How often the river goes over the point where additional monitoring is needed at primary contact sites | The mid-point (ie, half the time E. coli is lower than this, half the time it is higher) | E. coli only rarely goes past this point (only 5% of the time) | Risk of Campylobacter infection (based on E.coli indicator) |
| A (Blue) | <5% | <20% | ≤130 | ≤540 |
For at least half the time, the estimated risk is <1 in 1000 (0.1% risk) The predicted average infection risk is 1%* |
| B (Green) | 5-10% | 20-30% | ≤130 | ≤1000 |
For at least half the time, the estimated risk is <1 in 1000 (0.1% risk) The predicted average infection risk is 2%* |
| C (Yellow) | 10-20% | 20-34% | ≤130 | ≤1200 |
For at least half the time, the estimated risk is <1 in 1000 (0.1% risk) The predicted average infection risk is 3%* |
| D (Orange) | 20-30% | >34% | >130 | >1200 |
20-30% of the time the estimated risk is ≥50 in 1000 (>5% risk) The predicted average infection risk is >3%* |
| E (Red) | >30% | >50% | >260 | >1200 |
For more than 30% of the time the estimated risk is ≥50 in 1000 (>5% risk) The predicted average infection risk is >7%* |
* The predicted average infection risk is the overall average infection to swimmers based on a random exposure on a random day, ignoring any possibility of not swimming during high flows or when a surveillance advisory is in place (assuming that the E.coli concentration follows a lognormal distribution). Actual risk will generally be less if a person does not swim during high flows.
- Attribute state should be determined by using a minimum of 60 samples over a maximum of 5 years, collected on a regular basis regardless of weather and flow conditions. However, where a sample has been missed due to adverse weather or error, attribute state may be determined using samples over a longer timeframe.
- Attribute state must be determined by satisfying all numeric attribute states.
People should always check with their Regional Councils or the Land Air Water Aotearoa (LAWA) website for the latest information on whether it's safe to swim at popular swimming spots.
More information on the swimming categories for E. coli in the Clean Water package.
Lakes
The table below sets out the indicator involved in establishing an attribute state from Blue to Red for lakes.
The categories for toxic cyanobacteria (known as toxic algae) show the bio-volume of potentially toxic cyanobacteria present in each lake. We take a precautionary approach and assume that all cyanobacteria are toxic. Table 2 shows a definition of the categories, and the health risks for swimmers associated with each category.
These categories are based on Appendix 2 of the National Policy Statement for Freshwater Management 2014, and the 2009 Guidelines for Cyanobacteria in Recreational Fresh Waters.
There is insufficient data to model E. coli levels across all lakes. Where an individual lake has elevated levels of E. coli we have noted this on the swimming maps with a pop-up warning.
Table 2. The Cyanobacteria categories (attribute states) in detail
| Value | Human health for recreation | |
|---|---|---|
| Freshwater Body Type | Lakes and lake fed rivers | |
| Attribute | Cyanobacteria – Planktonic | |
| Attribute Unit | Biovolume - mm3/L (cubic millimetres per litre) | |
| Attribute State | Numeric Attribute State | Narrative Attribute State |
| 80th percentile* | ||
| A (Blue) | ≤0.5 mm3/L biovolume equivalent for the combined total of all cyanobacteria | Risk exposure from cyanobacteria is no different to that in natural conditions (from any contact with fresh water). |
| B (Green) | >0.5 and ≤1.0 mm3/L biovolume equivalent for the combined total of all cyanobacteria | Low risk of health effects from exposure to cyanobacteria (from any contact with fresh water). |
| C (Yellow) |
>1.0 and ≤1.8 mm3/L biovolume equivalent of potentially toxic cyanobacteria OR >1.0 and ≤10 mm3/L total biovolume of all cyanobacteria |
Moderate risk of health effects from exposure to cyanobacteria (from any contact with fresh water). |
| National Bottom Line |
1.8 mm3/L biovolume equivalent of potentially toxic cyanobacteria OR 10 mm3/L total biovolume of all cyanobacteria |
|
| D (Orange/Red) |
>1.8 mm3/L biovolume equivalent of potentially toxic cyanobacteria OR >10 mm3/L total biovolume of all cyanobacteria |
High health risks (eg, respiratory, irritation and allergy symptoms) exist from exposure to cyanobacteria (from any contact with fresh water). |
* The 80th percentile must be calculated using a minimum of 12 samples collected over 3 years. 30 samples collected over 3 years is recommended.
Water quality for swimming was modelled using the approach outlined in Strategic assessment of New Zealand's freshwaters for recreational use: a human health perspective.
Adjustments of model predictions
Adjustments were made to the predictions where the models didn't match actual data at a site.
Adjustments were made based on:
- expert opinion from freshwater scientists
- fact-checking with regional councils
- actual data at a monitoring site. River reaches were adjusted to account for data from monitoring sites. Changes were made at and upstream of the monitoring site if a category was incorrectly predicted (ie, a different result to the monitoring site)
- the values in surrounding river reaches. If one reach was surrounded by reaches with higher or lower category, the reach was changed to the predominant category to account for model error (ie, the reach was only just over or under a category threshold).
At the monitoring site level, there is some statistical uncertainty associated with each of the categories. On any one day a site could be in a higher or lower category for swimming.
There are also other factors which can affect how suitable a waterway is for swimming, including flow, access, heavy rain events, and other weather conditions. These maps don't provide advice on these.
For these reasons, always check regional council websites and the Land, Air, Water Aotearoa website for the latest conditions and warnings at popular swimming spots before you swim.
The methods used to model river and lake water quality for swimming for these maps are outlined in the following report: Strategic assessment of New Zealand's freshwaters for recreational use: a human health perspective. Escherichia coli in rivers and planktonic cyanobacteria in lakes.
Peer review of the methods
This report was peer reviewed by the Cawthron Institute.
For the review and the authors response to the review see: Review of Strategic assessment of New Zealand's freshwaters for recreational use: a human health perspective.
Related publications
Related pages
Water data for lakes, rivers and swimming spots on the LAWA website