NSW Department Primary Industries (DPI) Fisheries Deputy Director General, Sean Sloan said the zero-bag limit over this four-month period helps protect the native fish species while they spawn over the winter.

"During winter, these popular native sportfish species form large groups and migrate to parts of estuaries with the right salinity to trigger spawning," Mr Sloan said.

"After recent rainfalls across the state, it is important that fishers respect this closure from May 1 through to August 31, as the spawning period is key in the species' survival.

"This closure protects the fish during this spawning period to ensure they can remain a popular catch with recreational fishers for many generations to come."

Mr Sloan said that the zero-bag limit does not apply to Australian Bass and Estuary Perch caught in freshwater dams or in rivers above impoundments, as the fish do not breed in these areas.

"All fish in freshwater impoundments, like Glenbawn Dam and Glennies Creek Dam in the Hunter Valley, Brogo Dam near Bega and Clarrie Hall and Toonumbar Dams in the northeast, are stocked fisheries, meaning anglers may continue to fish for these species in these waters all year round," Mr Sloan said.

"However, any Australian Bass or Estuary Perch caught in estuaries and in rivers below dams during the closure must be returned to the water immediately with the least possible harm to the fish.

"The zero-bag limit for these species does not close any waters to fishing and does not affect anglers fishing for other estuarine species, such as bream or flathead during the colder months.

"Our DPI Fisheries Officers will be out in full force during this time."

If any suspected illegal activity is witnessed, the public are urged to contact the Fishers Watch Phoneline on 1800 043 536 or via the online report form here - https://fal.cn/3gJWh.

For more information regarding the annual closure, please visit the DPI's website - https://www.dpi.nsw.gov.au/fishing/closures.