Scientists are worried waterways in central western New South Wales, revitalised after weeks of flooding, will aid the spread of invasive species.
Following major flooding events in the Murray-Darling Basin during the 1970s and 1980s, the European carp was able to expand its population size to account for 90 per cent of the river systems biomass.
Andy Sheppard, biosecurity research director at the CSIRO, said a similar explosion in the fish's population could occur again after years of drought.
"They will be spreading back into areas they have been in previously, but have been knocked out of by the drought," Dr Sheppard said.
"With the flooding, they will be moving into wetlands that have not had water for five or six years and colonising those areas.
Dr Sheppard said the carp have had a massive impact on the native environment.
"The historic pictures of Australia's inland river system show clear, dark, and rich waters. Now most of them are just muddy," he said.
"The lack of sunlight really affects the growth of other water plants, and it upsets the balance of the food chain that supports many of our native fish.
"There have been massive declines in core species like Murray cod and some of the smaller natives which really shows a lot of it is associated with abundance of carp."
Weeds set to spread
The Central Tablelands Local Land Services said weeds, such as the sticky nightshade, have become established in the upper Belubula River system, near Canowindra.
Sticky nightshade is a prickly plant that can grow to more than a metre and a half in height and begins to bear fruit and seeds within six weeks.
The service's regional weeds coordinator, Marita Sydes, said the floods had washed the weeds further downstream.
"That area was impacted by the floods so that a lot of those sticky nightshade plants were possibly physically removed by the force of the floodwater and transported downstream of Canowindra and even into the Lachlan River," Ms Sydes said.
Ms Sydes said once it has taken root, the weed is costly and challenging to remove.
"Once it becomes established it is quite difficult to get rid of, just because it grows quite quickly, and it produces a fair bit of seed."
"Cost of control is one of the main issues; that cost being lots of man hours trying to get on top of it."
"Where it is quite well established in the upper Belubula a lot of landholders are spending a lot of time and a lot of man hours controlling and trying to contain it."
