Invasive threat choking Australia's rivers: 'Worst I’ve seen'

Carp already account for 90 per cent of fish in some rivers and they're gaining territory.

Thousands of kilometres of Australian rivers are clogged with unprecedented numbers of invasive carp that are stirring up nutrients, muddying waters and displacing native species.

Severe flooding across Australia’s Murray-Darling Basin has resulted in a breeding surge so severe the species accounts for 90 per cent of fish in some waterways. Videos shared to social media show green water choked with the dark bodies of carp.

Charles Sturt University’s Dr Ivor Stuart told Yahoo News Australia conditions are worse than during the 2010 and 2016 floods. “I’ve been working in the field for 30 years… and there’s been some bad years, but this is the worst I’ve seen.”

A river choked with carp.
Australia's carp invasion is the worst one expert has seen in 30 years. Source: Dr Ivor Stuart

Carp are following water downriver and into floodplains, where they breed and survive in high numbers. It’s when they head into the rivers that they’re running out of food and starving to death. It’s the Murrumbidgee, Darling and Macquarie Rivers that are worst affected, because it’s where floodplain litter has settled, making the waters nutrient rich.

How can Australia control invasive carp?

Despite having a boom and bust lifecycle, carp are gradually expanding their territory. While scientists have been successful in destroying them in Tasmania, on the mainland they are thriving. Dr Stuart warns they could spread into the tropics, into the Snowy Mountain’s pristine mountain streams, and new parts of Western Australia.

A researcher holding a carp to camera.
Bio-control is the main technology available to control carp. Source: Dr Ivor Stuart

With the problem now at a national scale, scientists will need to use multiple techniques to help reduce their numbers. While bio-control through viruses is a technology that’s currently available, gene modification is probably a decade away, Dr Stuart believes.

Outlining the risks in an article for The Conversation, Dr Stuart notes a major risk is short-term deterioration of water quality and its impact on native species. Benefits include long-term recovery of ecosystems and a return to biodiversity.

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