The reason for numerous dead snapper and a strange white film in a Kaipara river is currently a mystery.

Northland Regional Council (NRC) is unsure whether the two are linked but this week sent samples of the film to the Cawthron Institute for scientific testing.

Environs Te Uri o Hau – the environmental arm of Te Uri o Hau Settlement Trust – has begun its own investigation after whānau reported finding dead fish from Batley Point north down the Ōtamatea River.

Environs said online that with the support of Ōtamatea Marae, it had sent staff (kaimahi) to collect samples of the water and dead fish. Those samples had now been sent for independent testing, the results of which would be shared directly with marae and whānau as soon as they were available.

At this stage, Environs stressed no cause had been confirmed and no link had been established between the dead fish and any consented activity in the catchment.

It cautioned the public to avoid harvesting kai moana from any areas where dead fish were visible.

The Ōtamatea Awa is a significant waterway for Te Uri o Hau, flowing south of Maungaturoto and past the Ōtamatea Marae on Tanoa Rd before joining the northern arm of the Kaipara Harbour. It is a key source of food, recreation and cultural practice for hapū, and environmental concerns in the area are taken seriously.

Research has shown that the Kaipara Harbour is a nursery for 98% of the snapper on the west coast of the North Island.

The regional council said it, too, was acting after reports from the public of dead snapper in the Ōtamatea River and a white film visible along the tideline. Group manager – regulatory services Colin Dall said council officers notified MPI of the fish deaths and began inspecting major discharges within the catchment, including Fonterra’s Maungaturoto dairy factory and two Kaipara District Council wastewater treatment plants.

A council compliance officer visited the area on February 24 and observed the film. It initially appeared as green fibres, but when touched, it turned into a white powder. No dead fish were seen during that visit, but NRC had received photographs showing numerous dead snapper in the river at about that same time.

The officer deployed a drone to survey the river, but the footage did not show any white film present in the water. Samples of the material and surrounding sediment were collected and are now being analysed at Cawthron.

A sample of a strange white film that recently appeared in the tideline of the Otamatea River has been sent for scientific testing. Photo / NRC

One possibility being considered was that the material might be dead diatoms – a type of microscopic algae commonly found in marine and freshwater environments.

NRC said there was nothing at this stage to confirm that the white film and the snapper deaths were connected. It noted that only snapper had been reported. No other species were found dead.

Dall said that given fish were generally able to avoid areas of poor water quality, one possibility being considered was that the snapper were dumped, either inadvertently or deliberately.

Both investigations – from NRC and from Environs Te Uri o Hau – are ongoing.

Environs has asked anyone who sees further dead fish or unusual material in the water to report it so the information can be included in the iwi’s monitoring effort. Reports can be made via Facebook Messenger, by emailing [email protected] or by calling 0800 ENVIRONS.

The Advocate was unable to contact Environs directly within the timeframe for this article.

Sarah Curtis is a news reporter for the Northern Advocate, focusing on a wide range of issues. She has nearly 20 years’ experience in journalism, most of which she spent court reporting in Gisborne and on the East Coast.