Cause of Gold Coast mass fish kill unknown with marine heatwave most likely culprit, scientists say

Local community group says whatever the cause ‘kids shouldn’t be in the water’ with dead fish

Queensland authorities are investigating the deaths of thousands of fish that washed up on a popular Gold Coast beach.

The state environment department said dead baitfish had been observed at The Spit, at the northern end of the Gold Coast since last Wednesday, but no obvious source of pollution had been found.

A spokesperson said water quality monitoring “indicated high water temperature and low dissolved oxygen in the area”, which can cause fish deaths.

Concerned locals posted videos showing dead fish along the shores of the popular spot over the weekend and expressed frustration that warning signs did not appear to be in place for swimmers.

The president of Save Our Southern Gold Coast, Kath Down, said “there were thousands of fish that had obviously been there a long time”.

“It smelt terrible. They were all throughout the water and up on the high tide line,” she said.

Down was concerned families with young children were swimming in the area, particularly when the cause of the incident was still being established.

“We don’t know what they died of – whether they were chased by a predator or there wasn’t enough oxygen – but kids shouldn’t be in the water with them,” she said.

A Gold Coast city council spokesperson said water quality testing had shown “the water is safe for swimming but we are asking people to avoid the area while clean up is under way”.

“The City is working with the Department of Environment, Tourism, Science and Innovation to investigate this matter,” they said.

Dr Leonoardo Guida, a marine biologist at the Australian Marine Conservation Society, said although authorities were still determining the cause of the fish deaths, “early reports suggest they are temperature-related and as a consequence there is low oxygen in the water”.

Guida said, generally speaking, the body temperature of fish was “dictated by the water”.

As the temperature of the water rose, the activity levels of the fish increased and they required more oxygen.

“If you’ve got water that gets so hot that it doesn’t have enough oxygen to support that, the fish literally choke to death,” he said.

In recent years, Australia’s oceans have experienced record high temperatures.

Guida said higher ocean temperatures were affecting marine life around the country, pointing to the mass marine deaths from South Australia’s algal bloom and coral bleaching off Western Australia, including at Ningaloo Reef, as recent examples.

He said such events affected biodiversity, communities and economies and emphasised the need for a fast transition to net zero. He said policies to help build resilience in marine species populations, including species that were commercially important, would be essential.

The Queensland environment department’s spokesperson said council staff had collected water samples and results would be reviewed as soon as they became available.

They encouraged members of the public to report any fish deaths to the department’s pollution hotline on 1300 130 372.

Cover photo:  Thousands of dead fish have washed ashore on the Gold Coast, with high water temperatures believed to be the most probable cause. Photograph: Save Our Southern Gold Coast/Kath Down