“The initial findings of our investigation are that the work undertaken by the ORC Operations team complied with the permitted activity criteria in ORC’s Coast Plan,” General Manager Regulatory Richard Saunders said.

“ORC is now engaging an independent party to review the findings of the investigation. Having a qualified third party evaluate these findings will provide an independent assessment of the legality of the activity.”

Mr Saunders said a scientific analysis could not identify an exact cause of the fish deaths, but found that the opening of the coastal mouth was a possible factor, alongside degraded water quality and increased water temperatures.

“The Kaikorai is known to stratify in deeper locations of the estuary, meaning there is a warmer top layer of water with higher dissolved oxygen levels, and a colder layer with lower dissolved oxygen levels. Opening the mouth may have allowed the oxygen-rich layer to drain out of the estuary, exacerbating natural factors such as temperature and algal growth.”

Under the new National Policy Statement for Freshwater Management 2020, ORC will be required to develop an action plan to halt water quality degradation and improve the health of water bodies that do not meet NPSFM bottom lines.

ORC’s Engineering team has engaged independent expertise who are assessing the incidents at the Kaikorai Estuary and Silverstream.