2025 catchment monitoring update – encouraging signs for Lake Hayes

The latest 2025 results (386t) indicate that sediment loads entering the lake from Mill Creek remain well below the historic levels estimated in earlier studies.

Prior to 2020, catchment investigations suggested that around 1,000 tonnes of sediment per year could reach the lake under typical conditions. Our long-term restoration goal has been to reduce that figure toward a rolling average of around 300 tonnes per year, a level considered more consistent with supporting a healthier lake. Recent monitoring shows that, despite increasingly variable weather patterns, sediment loads are trending closer to this target.

Because each tonne of sediment typically carries around 1 kg of phosphorus, reducing sediment inflows directly reduces the nutrient supply that can drive algal blooms. The lake also enjoyed a clear “blue lake” summer, demonstrating how quickly water quality can respond when nutrient pressures are reduced.

The removal of approx 3,200 tonnes of sediment from Mill Creek and upstream areas has reduced a significant store of nutrient-rich material that would otherwise have continued entering the lake during storm events.

However, lake restoration is a long-term journey rather than a single project. Rapid land-use change in the catchment, particularly the shift toward more urban development, means that stormwater management is now one of the most important factors influencing the lake’s future health.

By using nature-based stormwater systems, such as wetlands, infiltration areas, vegetated swales and sediment traps – runoff can be slowed, filtered and cleaned before reaching streams.

A simple guiding rule is being promoted across the catchment: All stormwater leaving individual properties should have very low water cloudiness (less than 5 FMU). In simple terms, this means that stormwater leaving a property should be almost clear, indicating that sediment has been effectively captured before the water reaches drains or streams. This standard, combined with ongoing visual monitoring of waterways, allows problem areas to be quickly identified and remedied before significant sediment reaches the lake.

The recent monitoring results show that remediation efforts are making a real difference. With continued attention to sediment control and stormwater management, the community can look forward to more frequent blue-lake years while steadily improving the long-term resilience of the lake

Wai Whakaata/Lake Hayes is showing that when a community manages catchment remediation, sediment and stormwater well, a lake can recover.