Marlborough’s lakes have been under scrutiny following recent water quality assessments, revealing a mixed picture of health across the region.
The Marlborough District Council’s monitoring efforts, prompted by the 2020 National Policy Statement for Freshwater Management (NPS-FM), have highlighted both challenges and opportunities for improvement.
Lake Elterwater, situated in the Flaxbourne-Mirza-Waima (Ure) area, is the largest surface water body in this region and holds ecological importance. Historically, the lake has experienced frequent drying periods, with records showing it has dried up ten times in the past century. The 2016 Kaikōura Earthquake further altered its hydrology by tilting the lake, increasing its water storage capacity and extending the duration it retains water.
Despite its ecological significance, Lake Elterwater faces substantial environmental challenges. It lacks an outlet for water flow, making it prone to accumulating pollutants and nutrients, which can lead to algal blooms. The lake’s health is further compromised by high levels of nitrogen and phosphorus, consistently exceeding national standards. These conditions are worsened by its shallow depth and low rainfall catchment area, receiving less than 700mm annually.
A local catchment group is actively engaged in improving Lake Elterwater’s condition, focusing on planting native vegetation and developing a comprehensive management plan. The Taimate Trust has also been involved in restoring native vegetation around the lake, recognising its status as Marlborough’s second-largest freshwater wetland.
In contrast, more remote lakes like Lake McRae, Bowscale Tarn, and Lake Chalice generally exhibit better health, with Lake McRae receiving an A grading for its water quality. These lakes benefit from fewer human impacts and more pristine conditions.
Grovetown Lagoon presents another case of environmental concern, with phosphorus levels nearing the D-band due to invasive species like oxygen weed. Managing phosphorus sources in the surrounding area is crucial to mitigating these issues.
The council is considering expanding its monitoring to include other water bodies, such as Argyle Pond and Lake Grassmere/Kapara Te Hau.