Some of Brazil's beaches have been covered by a "tsunami" of rubbish, leaving once pristine coastlines completely engulfed in everything from plastic bags and bottles to children's toys and dead fish, Brazilian environmentalists have said.

On a tour of a beach just 20 kilometres from Rio de Janeiro's iconic Copacabana, environment protection activist Ricardo Gomes explained the gravity of the situation as he tried to clean up some of the waste on Isla do Catalao.

"These are the 8 million tonnes of plastic that reach the ocean each year, suffocating marine life and threatening the existence of Man on the planet," Mr Gomes said.

"This is a crime, it is not just a crime against the City of Rio de Janeiro, it is not a crime only against the population of Rio de Janeiro. This evil that we do in Rio de Janeiro, what the people of Rio de Janeiro do, what we do to the Ocean is a global crime," he added.

Mr Gomes is the president of Brazilian environmental protection group "Mar Urbano Institute" and his campaign to save Rio's beaches garnered international attention when videos he recorded of the plastic pollution were shared by world surfing champion Kelly Slater on his Instagram feed.

"70% of all this plastic here on the beach is made up of single-use plastic," Mr Gomes said.

"From disposable containers to plastic cups and food containers and we can change that. We can buy food in a restaurant that doesn't use plastic containers, we can reduce the consumption of plastic within our home and within our own lives," he added.

According to Oceana Brazil's report, the South American country throws some 325,000 tons of plastic into the sea and the pollution affects some 100 coastal lagoons of the Rio de Janeiro State coast, according to the Baia Viva environmental movement.