The grey nurse shark was detected by a Forster Dive Centre diver at Seal Rocks in NSW which captured the footage and shared it on their Facebook page.

"She's been living with what looks to be a round ring of plastic similar to a frisbee and it's cutting badly into her body," a Facebook post from Forster Dive Centre said.

"She's about 1.6m long and probably won't survive too long like this.

The video shows a large gash along the 1.6 metre shark's back.

"She's going to lose her ability to manoeuvre around the ocean the way she should be in her natural habitat and eventually it's going to become difficult to hunt," dive centre co-owner Adam Clarke said.

"It's going to keep cutting into her skin and so could cause even more nerve damage."

Grey nurse sharks are a protected species with an estimated population of 3000 along the east coast of Australia.

Following the sighting, Mr Clarke emailed the NSW Department of Primary Industries, texted contacts and lodged an online report.

However, he is yet to hear back.

Mr Clarke and co-owner Amelie Chipeaux have used the incident as a reminder for beachgoers to 'take 3 for the sea' by picking up three pieces of rubbish every time they leave the beach.

"Be more diligent with your rubbish, pick up after yourself," Mr Clarke said.

"Pick it up and put it in the bin, because it's only going to end up in the ocean."

UNESCO estimates there are 50-75 trillion pieces of plastic and microplastics in the ocean.

It believes that by 2050 plastics will likely outweigh fish in the sea.