Annual water quality results continue to guide action in Upper Waitaki
Our latest annual water quality monitoring results show a mixed picture for lakes and rivers in the Upper Waitaki catchment—information that is already shaping how we manage land and water in this area.
Each year, we monitor nine lakes and 14 rivers in this special part of Waitaha Canterbury to help us understand long-term trends and guide decisions about resource consents, land management, and environmental protection. The results were shared with our Regional Delivery Committee this week.
“The Upper Waitaki catchment is a particularly special area – treasured by many for its outstanding natural features, rivers and lakes and habitat for native species like the kakī black stilt and tiny galaxias fish, as well as traditional mahika kai resources,” said Dr Elaine Moriarty, chief scientist.
“It also contains a very high proportion of Waitaha Canterbury’s natural wetlands, many of which are being managed very well by landowners. The planning limits in this area are set to reflect the importance of protecting what is there now, and are based on the sensitivity of high country lakes and rivers.”
Annual monitoring results
Lakes
- 6 out of 9 lakes met water quality limits.
- Lake Alexandrina, Aviemore, and Kellands Pond exceeded limits.
- Lake Benmore's Ahuriri Arm Trophic Level Index (TLI) is above the early warning trigger, which means some farms need to take action to reduce nutrients.
- Lake Alexandrina, Lake Aviemore, and Kellands Pond exceeded their limits this year—a trend that has continued since 2020.
Rivers
- 9 out of 12 river sites exceeded nitrate limits.
- 4 sites exceeded phosphorus limits.
- Twizel River showed a sharp increase in nitrate levels this year.
- Other rivers like the Ahuriri, Willowburn, and Wairepo Creek continue to show persistent high nutrient concentrations.
Impact on freshwater health: Rising nutrient levels in rivers can flow downstream, increasing pressure on lakes and contributing to declining freshwater quality.
Why are TLI limits used to measure lake health?
- Exceeding TLI limits increases risk to mahika kai, recreation, drinking water, and ecological values
- Water quality results inform new and pending consent decisions
TLI is calculated using data on nitrogen, phosphorus, and chlorophyll A (a pigment found in algae). The measurement is not used for recreational water quality (swimming water quality is measured differently) but it’s a reliable indicator of overall lake health.
Action underway
Pim de Monchy, water and land manager says, "We are actively responding to these results—and those from previous years.
“Water quality results like these are a key consideration for any new or pending consent applications. Consent holders whose activities contribute to nutrient levels may be required to reduce their impact if their conditions require it—and many farmers in the wider catchment are already involved in voluntary initiatives including habitat protection, riparian planting and stock management to reduce nutrient losses.”
In the Ahuriri Catchment (near Omarama) there is a dedicated land management project underway. This includes:
- wetland and habitat protection
- improved management of critical source areas
- catch cropping trials to reduce nitrogen leaching following winter grazing
- investigating woodchip bioreactors
- willow removal from sensitive areas.
This long-term project is working alongside our Rūnanga partners, landowners, and local catchment groups to reduce nitrogen losses and protect the long-term health and cultural values of Lake Benmore and surrounding waterways.
The Love Our Lakes campaign also covers the Upper Waitaki area to raise awareness of environmental responsibility for all visitors and lake users, and encourage community action.
Dr Elaine Moriarty added: “While the suite of actions underway and planned will make a helpful contribution to reduce nutrients, overall ecological improvement will take time and commitment from many parties."
“Meanwhile, our monitoring will continue, and results will help guide future decisions about land use and water management in this sensitive and valued catchment,” said Dr Elaine Moriarty.
Community engagement
Consent holders that need to take action have already heard from our team, and we’ve also met with the local Ahuriri catchment group. A community information session for the whole Upper Waitaki catchment is being planned for early summer. This will include updates on our other work, including planning for this year’s Love Our Lakes campaign.
You can read more about the Ahuriri project and Love Our Lakes on our website.