Seabirds at Montague Island off Narooma have stomachs full of plastic, one of Australia's leading wildlife biologists has warned.

Macquarie University professor of marine ecology Rob Harcourt has worked with the seabirds of Montague Island for many years. He is very familiar with the growing of problem of loose, floating plastic in the world's oceans and how that pollution is impacting on marine animals.

Birds at Montague Island off Narooma. Credit:Nick Moir

"There is a large colony of seabirds breeding on Montague Island and plastics look a lot like their food items," Professor Harcourt said.

"They [the birds] pick up the plastics instead, because they look like fish. They take it back to feed their chicks, and the chicks starve because their stomachs are full of plastic. It's a serious, serious problem."