It is the fish that Canberra loves to hate.
But there's a new biological weapon that potentially could decimate its numbers in Lake Burley Griffin - provided it doesn't create an ecological disaster in the meantime.
Carp (Cyprinus carpio, also referred to as common carp) are one of the worst introduced pest species in Australia.
There are thousands of carp in Lake Burley Griffin and throughout most of Australia's inland waterways, particularly in the Murray Darling Basin where they make up between 80 to 90 per cent of the fish biomass.
Carp have had a devastating impact on biodiversity and have decimated native fish populations in many areas since they first became established in the 1960s.
But now there's a fresh new weapon against the insidious carp menace - a specific herpes. The agent is known as Cyprinid herpesvirus 3 (CyHV-3), or simply the 'carp virus'.
The Australian government has committed over $10 million toward the National Carp Control Plan since 2017.
Technical papers for the potential implementation of the carp virus reveal that most of the studies are now complete and now it is only for the states and territories to agree on a strategic plan for its release.
However, the current La Nina weather pattern, which has brought unseasonal wet weather to the eastern states and flooded many inland waterways, presents unsuitable release conditions.
The plan's technical papers recommend it to be released "during a dryer climatic period when carp populations are both reduced and concentrated at known aggregation locations".
The carp virus is water borne and highly contagious.
The first signs of it are a reddening of the gills, excess mucus on the gills, darkening of the gills and finally tissue necrosis. Carp usually die within 7-14 days of the virus being introduced to their habitat.
Carp that survive infection are infected for life, and when stressed may die or show signs of disease again. These fish are capable of spreading CyHV-3 to other carp.
CSIRO testing has shown that it posed no danger to 13 native species such as Murray Cod, various species of perch, eel and catfish, as well as a crustacean (yabbies) and a non-native fish species, the rainbow trout.
But the big danger in releasing the virus is widescale carcass management as a lake full of dead and decomposing fish has the potential to create a toxic environment for everything else living within it, including Murray cod and perch.
Netting all the dead fish would have to be done expeditiously.
Former Canberra fisher Anthony Heiser, who was a committee member of the Canberra Fisherman's Club for 11 years, has studied the control plan and says that any lakes, reservoirs and slow-moving inland water bodies with more than 300 kilograms per hectare of carp volume were at risk of depleted oxygen levels and toxic algae blooms.
Canberra's lakes have carp densities far exceeding this level: between 380 kilograms per hectare and 588 kilograms per hectare.
"One issue [the plan] was unable to address was how and where accumulated nutrients from decomposed carp would get trapped in river and lake sediments and the potential for those nutrients to contribute to future toxic algal blooms," Mr Heiser wrote.
"Given carp biomass fluctuates in response to flood or drought conditions, the timing of initial virus deployment needs to be carefully planned to ensure the quantity and concentration of dead carp do not lead to unmanageable environmental and water quality risks."
Fortunately, the chosen approach to releasing the virus appears to be one of caution.
In the US, the introduction of the virus to the upper Mississippi River since 2017 has driven carp populations down and helped native fish numbers rebound.
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