The Nature Coast Marine Group says the lifting of the block on recreational fishing in six areas of the unique Batemans Marine Park threatens to destroy important parts of a unique environment stretching from Murramarang Beach near Bawley Point to the southern side of Wallaga Lake entrance at Murunna Point.

One of the country's leading scientists added his voice to the debate over "no take" zones where fishing was once banned but is now allowed.

Professor Hugh Possingham, a world authority on special marine parks, said these protected stretches of ocean helped fish grow and would actually help fishermen.

"There's an enormous advantage in having protected areas where you get those very, very big fish, because they are ridiculously productive and they basically provide benefits for fishermen of stabilising the supply of fish and also, every now and then, they move out of those places and you get to catch an enormous fish," Prof Possingham said.

"You just don't get that if you're fishing everywhere."

The NSW government called the marine park "unique", citing "the large expanses of rocky reef that support a diverse array of fish, invertebrates and algae. Rocky shores, offshore rocky reefs, kelp beds, seagrasses, mangroves, sponge gardens, sandy beaches, estuaries and open waters are key habitats".

In December last year, the NSW government announced changes that increased recreational fishing in six areas. Other "sanctuary zones" remained closed to fishing.

But campaigners said damage was being done. "When you remove full protection, the larger fish are fished out," Bill Baker of the Nature Coast Marine Group said.

They've started campaigning under the banner "Save Batemans Marine Sanctuaries".

"Since these sanctuaries were opened up to fishing in December 2019, bushfires and COVID have placed extraordinary pressure on our South Coast environment, communities and tourism," Mr Barker said.

"We know that Canberrans care about the South Coast's marine heritage and coastal lifestyle.

"The sanctuaries were put in place 13 years ago to allow marine life to flourish undisturbed and to protect crucial feeding and fish nursery areas."

The campaigners said the change was made because of the pressure on the NSW government from the recreational fishing lobby.

A NSW Fisheries survey in 2000 estimated there were fewer than 300 grey nurse sharks left on the NSW east coast.

Conservation groups said recreational fishing was the main threat to the shark when it was accidentally hooked.

Humane Society International marine biologist Lawrence Chlebeck said the species would never have any hope of recovery if such threats were allowed in critical habitats.

"We must provide a sanctuary from hooks from which the species can rebuild," he said.