Upper Waitaki water quality results drive ongoing action

Our latest annual water quality monitoring results have provided an updated picture of lakes and rivers across the Upper Waitaki catchment, showing where freshwater systems remain under pressure, and are helping to guide environmental management decisions, and catchment improvement initiatives.

Each year, Environment Canterbury monitors nine lakes and 15 river sites across the Upper Waitaki catchment to understand long-term trends and assess water quality against the limits set in the Canterbury Land and Water Regional Plan.

Dr Elaine Moriarty, manager of Water and Land Science at Environment Canterbury, said the annual results provide an important evidence base for understanding the state of freshwater across the catchment.

“The Upper Waitaki catchment is one of Canterbury's most outstanding natural environments, valued for its iconic lakes and rivers, significant wetlands, unique biodiversity and important cultural values,"

"These annual results help us understand how water quality is changing over time and where action is needed to protect these highly valued freshwater ecosystems."

The annual water quality monitoring results focus on lake and river ecological health. This information is different to recreational water quality water grades, which assess suitability for swimming and are released ahead of summer.

Annual monitoring results

Lakes

The report focuses on the Trophic Level Index (TLI) of lakes, which is a measure of lake health based on nitrogen, phosphorus and chlorophyll-a, a pigment found in algae. Increasing TLI values indicate a greater risk of algal growth and declining lake health.

• Six of the nine lakes, including Pūkaki, Benmore, Takapō and Ōhau, met their TLI limits in the Land and Water Regional Plan
• Lake Alexandrina, Lake Aviemore and Kellands Pond exceeded their Trophic Level Index limits
• Lake Benmore's Ahuriri Arm exceeded an early-warning trigger contained in some resource consent conditions but remained below its regional plan limit
• Ten-year trends show increasing total nitrogen and chlorophyll-a concentrations in seven of the nine lakes assessed, which can contribute to nuisance algae formation.

Rivers 

Nutrients in rivers can contribute to downstream pressure on lake ecosystems. High nutrient concentrations are also an issue for the river themselves, with risk of nuisance algae and aquatic plant growth damaging river ecosystems.

Monitoring of 15 river sites 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 regional plan limits exceeded nitrate-nitrogen limits.
• Three sites exceeded dissolved reactive phosphorus limits.

Understanding the long-term trends 

While annual results naturally vary from year to year, the longer-term monitoring record provides important insight into how freshwater ecosystems are responding to land use and environmental pressures across the catchment.

"Looking across a ten-year period gives us a clearer view of the direction of travel, beyond the natural variation we expect to see from year to year," Dr Moriarty said.

"Where we see nutrient concentrations and algae-related indicators increasing, it helps focus attention on the areas where continued effort will make the greatest difference for water quality."

Action underway

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.

Within the Ahuriri catchment work is underway in collaboration with landowners, including:

• wetland and habitat protection
• improved management of critical source areas
• catch cropping trials to reduce nitrogen losses
• willow control in sensitive waterways.

Consent holders that need to take action will hear from our team, and we’re also meeting with local catchment groups to share results, discuss trends, initiatives and compliance expectations.

To read the report and find out more our water quality monitoring in Ahuriri and Upper Waitaki head to our webpage.