The Lower Murray could become a bloody mess filled with as many nutrients as sewage if the National Carp Control Plan (NCCP) goes ahead, scientists have told a parliamentary hearing in Canberra.
Six experts, including Coorong district ecologist Faith Coleman, expressed numerous concerns to the Senate committee responsible for overseeing the NCCP on June 25.
University of Exeter researcher Jackie Lighten said infected carp would "profusely" leak blood into the water under a plan to control the pest species' population using a herpes virus.
"There will be lots and lots of blood in the river," he said.
"The quality of the water of the Murray-Darling Basin, if this goes to plan, would be comparable to sewage in terms of the levels of different nutrients in the river."
Biologist Adrian Falconer said politics appeared to have influenced the NCCP's direction, to the detriment of the Lower Murray.
"While the impacts (of a virus) will be felt throughout Australia, the majority of any potential benefits will be delivered to upstream water users, while the majority of risks fall to those living in downstream communities - people already heavily impacted by disruption to our rivers, lakes and Coorong," he said.
If there were two million tonnes of carp in the river system and the virus killed 80 per cent of them, Mr Falconer said, there would be "very real dangers for total ecosystem loss".
"The rotting fish would consume more than four times the available dissolved oxygen in the water, with lethal impacts for other organisms sharing the water body," he said.
"To have any chance of keeping nutrients within the set guidelines ... 50pc to 90pc of carp biomass would need to be removed within 48 hours of death.
"Logistics render than prospect all but impossible."
However, he noted, the NCCP had not yet estimated how many carp were in the system - the actual figure could be 500,000 tonnes or six million.
The six experts also flagged flaws in some of the science underpinning the NCCP, including work around the impact of dead carp on water quality and the likelihood of other species being infected.
Ms Coleman said the NCCP had to be delayed until more data became available, a point seconded by Queensland ecologist Jonathan Marshall.
"I don't think we actually need to rush into this decision," Dr Marshall said.
"The problem isn't worsening ... likewise, I believe the potential of the herpes virus to act as a bio-control solution would not diminish if the decision timeframes were extended.
"There's no rush."
A draft is scheduled to be released this month.