Upper Waitaki water quality results
Each year we produce an annual report summarising data from the regular monitoring of nine lakes and 15 river sites across the Upper Waitaki catchment.
Why we monitor water quality
The Upper Waitaki contains sensitive high-country rivers, lakes and wetlands valued for their outstanding natural features, ecology, recreation and cultural significance.
Regular testing helps us track long-term changes in water quality, understand pressures on rivers and downstream lakes, and use the results to guide consent decisions, land management and actions to protect freshwater health.
This monitoring provides scientific evidence that helps us:
- understand long-term trends and where action may be required
- assess water quality against limits and consent conditions set in the Canterbury Land and Water Regional Plan.
The water quality report is different from reporting on recreational water quality water grades, which assess suitability for swimming.
Explore the lake and river results
Lake water quality
Results relating to lake water quality in the Upper Waitaki water quality report are based on the nationally recognised Trophic Level Index (TLI), a measure of lake health that capture:
- Nitrogen
- Phosphorus
- Chlorophyll-a, a pigment found in algae.
Increasing TLI values indicate a greater risk of algal growth and declining lake water quality.
The 2025/26 report found:
- Six of the nine lakes monitored, including Pūkaki, Takapō and Ōhau, met TLI limits set in the Land and Water Regional Plan.
- Lake Alexandrina, Lake Aviemore and Kellands Pond exceeded their TLI limits.
- Lake Benmore's Ahuriri Arm exceeded an early-warning trigger contained in some resource consent conditions but remained below the catchment-wide Land and Water Regional Plan limit of above 2.9.
Ten-year trends from our water quality monitoring programme in the Upper Waitaki show increasing total nitrogen and chlorophyll-a concentrations in seven of the nine lakes assessed, which can contribute to increasing ‘greenness’ of a lake.
River water quality
Monitoring of 15 river sites during 2025/26 found:
- Several rivers continue to show elevated nutrient concentrations, increasing the risk of nuisance algae and aquatic plant growth.
- Seven of the 13 river monitoring sites with limits determined in the regional plan exceeded their nitrate-nitrogen limits.
- Three sites exceeded dissolved reactive phosphorus limits.
Data from the past decade shows increasing nutrient concentration trends in most long-term river monitoring sites in the Upper Waitaki.
While climatic conditions can contribute to year-to-year variation in river nutrient concentrations, widespread long-term increases in river nutrient concentrations remain a concern for river health and downstream lakes.
How monitoring informs consent decisions
Every consent differs in its specific conditions. However, in the Upper Waitaki many irrigation and farming land use consents have conditions that require consent holders to test and report on water quality – both the water quality of rivers and streams flowing through their property and the quality of lakes downstream of them.
Consent conditions are set to allow land use activity while protecting the environment, such as the unique and sensitive Upper Waitaki ecosystem, based on science and in alignment with the Canterbury Land and Water Regional Plan.
Consent conditions consider factors such as:
- Anticipated water-quality outcomes
- Modelling of land-use development
- Good management practice
- Lake consent limits
The Waitaki subregional limits relating to the Canterbury Land and Water Regional Plan mean:
- Consents in some areas, including the Haldon Arm of Lake Benmore, were allowed limited additional nutrient loading, which could result in a small change in water quality while also ensuring water quality outcomes were achieved.
- More sensitive receiving environments, including the Ahuriri Arm of Lake Benmore, had limits set to maintain existing water quality rather than provide for further development.
River consent limits
For consent conditions relating to rivers in the Upper Waitaki:
- Some increase in nitrate concentrations was anticipated after a review of, and a Plan Change, to the Canterbury Land and Water Regional Plan. This was due to permitted/consented land-use development and lag effects of existing land use.
- River water quality limits were set to ensure that river and lake outcomes would be achieved.
Science such as the Upper Waitaki Water Quality Report are important tools to track real world outcomes against anticipated outcomes.