Why are carp a problem in the Murray-Darling Basin?
European carp are an invasive fish that dominate many rivers in the Murray-Darling Basin. They muddy the water, uproot plants and compete with native fish such as Murray cod.
Carp were introduced to Australia in the 1800s, but a strain called Boolarra carp spread rapidly through the Murray-Darling system after the 1960s, helped by floods. In some areas, carp make up most of the fish biomass in the river.
Carp feed by sucking up mud from the riverbed, stirring up sediment and making the water cloudy. This harms water plants, insects and native fish that need clear water.
Control ideas
Scientists have studied a carp herpesvirus as a possible biological control. The National Carp Control Plan investigated its risks and benefits.
Other methods include carp traps on fishways, which separate carp from native fish, and commercial fishing.
Anglers are encouraged not to return carp to the water.
Carp numbers boom after floods, when they spawn on flooded plains, and large fish kills have occurred during droughts and hypoxic blackwater events. Restoring river flows and habitat is seen as part of the long-term solution for native fish.
Did You Know?
Carp can survive in water with very low oxygen, which helps them thrive where native fish struggle.