Hundreds of dead fish removed from Heathcote River almost a week after first reports

Hundreds of dead fish in Christchurch’s Ōpāwaho Heathcote River were finally removed on Tuesday, nearly a week after initial reports of a mass die off.

There are still no answers on what caused the deaths, first reported to Environment Canterbury (ECan) on Wednesday, as it continues to test for possible culprits.

Spokesperson Nathan Dougherty said those recovering the corpses on Tuesday reported counting “at least 300”, with more still to retrieve.

It would be difficult to get a final tally, as it was likely “seagulls had picked up the odd one and lifted them out of the river,” and there were “definitely some that may have gone down to the estuary”.

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There had been no move to retrieve the dead fish earlier on the advice of ECan scientists, he said.

“We could have started earlier … but initially it didn’t seem likely that it was necessarily going to affect other wildlife.”

ECan was “not sure whether other animals have been affected”.

Dougherty was aware of a report that a seagull may have been affected, but “hadn’t tracked down” the vet who made that assessment “so we don’t know if it’s true”.

People were advised to stay away from the Ōpāwaho Heathcote River in the area of Connal St, Cumnor Tce, Long St, Garlands Rd until further notice.

The incident was a high priority for ECan, Dougherty said.

Linwood city councillor Yani Johanson said he was disturbed by “the lack of meaningful communication with the local community”, was “deeply concerned about the impact on wildlife”, and wanted to know what was being done to monitor and mitigate the contamination.

He had made several requests for information since news of the contamination became public, but had received only brief public updates.

Johanson said he saw significant numbers of people about last week and no visible information on what had occurred, so printed and put up his own warning signs.

On Monday, he found a young black back gull in distress on the berm near Long St, which he took to a vet, where the bird died.

The vet’s initial verdict was that the death could be related to the mass fish die off, he said.

Dougherty rejected any suggestion the response was not sufficient, or could benefit from assistance from other agencies.

“[The Ministry for the Environment] doesn’t have expertise in this area. We’ve got three experienced investigators working on it – these are folks who really know what they’re doing.”

Dougherty said an oil absorbent boom and an oil barrier boom had been installed at a major storm water outfall as a “preventative action”.

ECan had taken water samples and was getting advice from its scientists on next steps.

Dougherty said he could not say when results might be available.

He was not sure if the pollution had been contained or how long the water would be off limits, but ECan would keep “a really active watch on the river”.

“If there are no other dead animals being seen, that indicates the cause of the fish death has ceased.”

He saw fish on Saturday morning swimming through the lower reaches of the Woolston Loop, he said.

“That was a good sign, but whether they were affected later on I don’t know.”

The call for public assistance regarding any “unusual or suspicious happenings” near the river did not necessarily mean the council was looking for deliberate or illegal dumping.

“These things do sometimes happen by mistake, sometimes they happen because people chose to discharge things into waterways.”

In 2020, eight of the 13 worst sites in rivers or streams in Christchurch were in the Ōpāwaho Heathcote catchment.