An investigation led by the Otago Regional Council strongly points to the fish having been electrocuted rather than poisoned by pollution or killed by disease.

ORC director of environmental monitoring and operations Scott MacLean praised the detective work by ORC and Otago Fish and Game staff who worked, together with local fishing guide Grant Adolf, to investigate the death of around 20 trout over several days.

While he and colleagues were collecting water samples for analysis, ORC environmental officer Richard Heyward noticed a submersible pump in a privately owned wetland adjoining the stream.

Mr Heyward recalled Fish and Game staff’s comment that it was as if “something” was causing a magnetic field attracting the fish, and realised that most of the dead fish had been reported in the vicinity of the pump’s intake.

After he talked to the adjacent landowner, an electrician checked the pump and found that it had a faulty float switch, sending current directly into the water and electrocuting the fish.

Because the pump wasn’t operating all the time, the fish were being affected sporadically.

Mr MacLean praised the landowner for getting the pump checked and then arranging to have it removed as soon as the fault was identified.

“It’s a great example of people working together,” Mr MacLean said.

Extensive water sampling in Mill Creek had found no high levels of chemicals or heavy metals except aluminium in the vicinity of the pump, he said. The dead fish were sent to the Cawthron Institute in Nelson, where autopsies showed no sign of poisoning or disease.

“It’s a relief to be able to confirm that water pollution was not a factor in these deaths and that there is a simple explanation and an easy solution in this case,” Mr MacLean said.

ORC provides a 24-hour hotline (ph 0800 800803) for the public to report environmental issues and concerns.

For more information contact

Scott MacLean
Director environmental monitoring and operations
ORC
Ph 0800 474 082 or 027 411 9459