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Water Quality Monitoring Report – Q3 2023

By 5 December 2023News

Water Quality Monitoring Report – July to September 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

  • A rain event in July 2023 (30 – 90 mm rainfall) resulted in increased turbidity in Lake Opuha at depth (two weeks) and at the surface (a few days)
  • Cyanobacteria (blue-green algae) health warning removed for Lake Opuha in July 2023 after 148 days.
  • The tributaries of Lake Opuha experienced increased suspended solids, nitrate-N and dissolved reactive phosphorus due to increased flows from the July 2023 rain event.
  • Increased nitrate-N and dissolved reactive phosphorus were observed in the Opuha, Opihi and Te Ana Wai rivers.
  • Macroinvertebrate Community Index (MCI) and Quantitative Macroinvertebrate Community Index (QMCI) scores for the Kakahu Riverin August 2023 did not show any effects of the OWL discharge.  Although the discharge was not occurring at the time of the survey, this is an important result as it indicates that there is no longer term (i.e. months after discharge ceases) effects of the discharge.
  • Longfin eel, upland bully and common bully were caught in the Kakahu River as part of the August 2023 ecological survey. These fish were identified both upstream and downstream of the discharge point.

Download the full report here.