Drought-breaking rains in 2010 filled the state's parched rivers, and the subsequent floods led to an outbreak of the invasive fish species, known as the rabbit of the waterways.

The chief executive of the Invasive Animals Co-operative Research Centre, Andreas Glanznig, said the carp competed with native fish for food and habitat.

''After the last major floods the number of new carp in the system increased by up to 4000 per cent,'' Mr Glanznig said.

According to the NSW Department of Primary Industries, carp were widespread through most of NSW, particularly in the Murray-Darling Basin and the rivers of the mid-north coast, and the central and southern tablelands.

In some places in the Murray-Darling carp make up 80 per cent of the fish biomass, Mr Glanznig said.

Females reach sexual maturity at three to five years of age and produce 1 illion eggs, on average, when they spawn each year. Males can procreate from two years of age, which means those fish born after the drought will be ready to reproduce this spring.

As bottom feeders carp increase water turbidity, which means less light reaches water vegetation, and they also consume the eggs of other fish and invertebrates.

European carp have been present in the state's waterways for more than a century. To manage the pest, the Department of Primary Industries place cages that collect carp while allowing native fish through to waterways.

Unlike in Europe and Asia, there is limited demand for carp as a food source in Australia.

Scientists at the CSIRO's Australian animal health laboratory in Geelong are testing a biological control for the pest.

A research veterinarian, Ken McColl, said their experiments had shown the carp herpes virus was highly specific to carp and did not affect native fish or other animals.

The team hope to have the virus ready for approval within three years.

The varieties of freshwater fish introduced into Australian river systems have increased from 22 to 34 in the past 20 years.