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Independent review agrees that wastewater from septic tanks is polluting Muri lagoon

Updated: Nov 24, 2020

Current system in Muri causing damage to the lagoon

Independent environmental institute NIWA has reviewed and agreed with the findings of the environmental investigations report on the Muri wastewater project, written by the PMU and various specialists.

Key findings from the Cook Islands Government’s PMU consultants were presented to the public in December 2018. The independent NIWA Review of this environmental investigations report has just been issued.

The key findings in the report are:

  • Nutrients from septic tanks entering the shallow groundwater and flowing into the sensitive Muri Lagoon are causing the algae problems.

  • Decommissioning on-site wastewater systems will help reduce the amount of nutrients going into the lagoon, in particular into the sensitive, still areas where seaweed has become a problem.

  • Removing coral debris on the reef or dredging the lagoon will not provide any significant improvement to the lagoon’s conditions in the still water zones, and would create other harmful effects.

  • Other catchment management practices to preserve swamps, protect stream banks and avoid sedimentation from land erosion will be complementary to the reticulation of wastewater.

NIWA’s agreement with the report’s findings further supports the need for a centrally operated wastewater treatment plant in Muri to treat and dispose of wastewater appropriately.

The PMU have now started more environmental investigations to help inform the wastewater treatment plant design and disposal method.

The environmental investigations summary report is available here

About the investigations

The Mei Te Vai Ki Te Vai environmental investigations were a collaborative effort between the Project Management Unit (PMU), the Cook Islands Government ministries and specialist sub-contracted consultants. These partners include the Cook Islands Ministry of Marine Resources (MMR), Southern Cross University (SCU), University of New South Wales (UNSW) and GNS Science.

Completed over 2017-2018, the investigations covered a wide range of areas including geology, hydrogeology (groundwater) and water quality, lagoon ecology, the lagoon’s physical characteristics and oceanography.

The investigations were designed to close the gaps in existing information, and identify why Muri Lagoon has degraded and what we can do to help, in the short and long term. We are using the results to support development of improvements to the Muri sanitation system, and a longer-term monitoring programme to assess wastewater impact on the environment.

NIWA is the New Zealand National Institute of Water and Atmospheric Research ( It is a Crown Research Institute. NIWA has undertaken a range of research projects in the Cook Islands on relevant topics including water quality.

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