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Water Quality Monitoring Report – Q2 2023

Water Quality Monitoring Report – April 2023 to June 2023

Opuha Water Ltd publishes its quarterly water quality reports for Lake Opuha and the wider scheme catchment to share with the community the results of our extensive water quality monitoring program.

Water samples are collected and analysed for nitrogen, phosphorus, chlorophyll-a, iron, manganese, heavy metals, pesticides, E. coli, cyanobacteria, water clarity, dissolved oxygen, pH, and conductivity.

River surveys for benthic periphyton (material attached to the surface of rocks in the water) are also undertaken to better understand river health and to quantify the coverage of cyanobacteria and nuisance algae. The specific parameters analysed at each site depends on the objectives of the individual sampling programs.

Publishing quarterly water quality reports shows that Opuha is taking water quality management seriously, and demonstrates leadership in the district’s collective responsibility for protecting and improving the mauri (life force, vitality) of te taiao (the environment) in the catchment area.

Key Findings

  • Macroinvertebrate Community Index (MCI) scores for the Kakahu River since 2008 show similar values upstream and downstream of OWL’s discharge location.
  • The cyanobacteria (blue-green algae) health warning was current for Lake Opuha during the reporting period but has since been lifted.
  • Quantitative Macroinvertebrate Community Index (QMCI) scores for the Kakahu River in 2022 showed similar values upstream and downstream of the discharge location. QMCI data for other years did show some differences.
  • Heavy metals and DDT concentrations in Lake Opuha surface sediments were of low ecological risk.
  • Moderate to small rain events during the reporting period resulted in short-term increases in turbidity in Lake Opuha (four days to two weeks).
  • Waitohi Stream/Devils Stream (a tributary of the Opuha River) was the likely cause of poor water clarity in the Opuha River at Gorge and Skipton Bridge when sampling was undertaken in June 2023.

Download the full report here.