The Paterson, Hunter and Williams rivers are swimming with carp, especially at the Seaham weir pool, which flows into Grahamstown Dam and is a major source of drinking water for Newcastle. 

The highly-contagious virus stays active in the water for up to three days and quickly spreads through the carp without harming other fish, or humans, according to researchers.

Correspondence obtained by Fairfax Media shows the virus will be rolled out in the river systems as part of a nationwide plan to manage the species.

Ellie Burke, who reeled in a 70 centimetre carp from the Williams river at Clarence Town this month, said they were easy to catch because there were so many of them.

Her father John said the fish, which broke her line and was too heavy to pick up, was only an average size.

“It’s a monster, but they get bigger than that … They are the cockroaches of the water,” he said.

“It’s the biggest fish I’ve ever caught,” Miss Burke added.

Mr Burke supported the roll out but questioned how it would be managed around the Seaham weir pool. 

“Something needs to be done, they have a devastating effect on the health of the river,” he said. 

“I don’t know how they’re going to do it at the weir pool – it’s where Newcastle’s drinking water comes from.

“I don’t think people would be happy knowing the herpes virus is going to be released into their drinking water.”

The NSW Department of Primary Industries said it could not answer Fairfax Media’s questions about the plan when contacted last week. It said it would respond after it spoke with its researchers.

Hunter Water said it was inappropriate for it to comment on the plan, but it expected to be consulted before the virus was released.

Carp stir up sediment when they feed and cause more turbidity, poor water quality, river bank erosion and impact upon native aquatic plants.