Algaecide chemical blamed for fish deaths

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Pierra WillixSound Telegraph
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Hundreds of koi and other carp species have died after the City of Rockingham treated the lake in Apex Reserve with an algaecide product which, in turn, reduced oxygen levels in the water, killing them.
Camera IconHundreds of koi and other carp species have died after the City of Rockingham treated the lake in Apex Reserve with an algaecide product which, in turn, reduced oxygen levels in the water, killing them. Credit: Supplied.

Hundreds of koi and other carp species have died after the City of Rockingham treated a lake with an algaecide product which, in turn, reduced oxygen levels in the water, killing them.

On the weekend of December 22 and 23, Shoalwater residents noticed what they described to the Sound Telegraph as “hundreds” of fish rising to the surface of the Apex Reserve Lake, all dead.

Rangers attended the site on the Monday and collected the dead fish.

City of Rockingham Mayor Barry Sammels said the water quality of the lake was “not of suitable condition” because of high algae levels that had developed in the lake in previous weeks, and to help improve the overall water quality of the lake in the long term, an algaecide product was added on Thursday, December 20.

“The product was more effective than initially expected, which resulted in the algae breaking down quickly,” he said.

“This, in turn, rapidly reduced the oxygen level of the water, having an impact on the fish in the lake.”

Mr Sammels said the exact number of fish removed from the lake was unknown but they were introduced species that had a negative impact on native species.

“The vast majority of the fish affected were introduced species including koi and carp, which are known to cause detrimental impacts to other natural species,” he said.

He said the deaths were contained within Apex Reserve Lake and no other bodies of water had been affected.

“The City has followed up with a number of water samples to ensure the lake returns to normal,” he said.

“Results from testing indicate that oxygen levels have returned to near-standard levels and the water quality continues to improve.

“Tadpoles and frogs are still present in the lake and no lasting impacts are expected.”

A Department of Water and Environmental Regulation spokeswoman said a member of the pub

“DWER has provided advice to the City of Rockingham to minimise any potential environmental risks and will continue to liaise with the City as required,” she said.

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