Department of Primary Industries Director of Fisheries Compliance, Glenn Tritton, said officers have seized a large amount of unattended illegal fishing gear in the Murrumbidgee River during the past few months.

"With the Murray crayfish season almost over, fishers are reporting low numbers of Murray crayfish in the Murrumbidgee River," Mr Tritton said.

The fishing seasons for Murray crayfish and Murray cod, a popular catch in the Macquarie River, both draw to a close at the end of this month.

"Fisheries officers have recently seized five fish traps, one crab trap and a 25 metre gill net," Mr Tritton said.

"Gill nets are illegal and indiscriminate in what they catch.

"They are a threat to sustainable fish populations, particularly threatened species and immature fish.

"Officers also seized an abandoned hoop net, which was found to be 'ghost fishing' with four Murray Crayfish entangled in the mesh."

Mr Tritton said there are harsh penalties for those caught fishing illegally.

"Possessing illegally taken fish or using an unlawful net or trap can result in hefty fines in NSW of up to $22,000 or imprisonment for six months or both or alternatively a $500 penalty notice for either offence," he said.

"Illegal nets and traps pose a serious threat to other air breathing animals that occur in and around our freshwater river systems such as platypus, tortoise, turtles, water rats and water birds."

Suspicious activity can be reported to Macquarie RiverWatch on 1800 748 379 or the Fisheries phone line 1800 043 536.