Melbourne’s Port Phillip Bay is being trashed, with an estimated 1.4 billion pieces of rubbish flowing into the sea annually from the Yarra and Maribyrnong rivers.

The new figures paint a confronting picture of environmental damage in the bay, but they also provide a ray of hope – a decline in plastic straws.

Monthly trawls of rubbish in the two rivers between January, 2015 and 2019, conducted by Port Phillip EcoCentre, showed microplastics made up almost 80 per cent of the rubbish entering the bay.

The calculated number of microplastics, fragments smaller than five millimetres in diameter, almost doubled in the collection period – from 612 million to 1.1 billion pieces.

The centre has been analysing tens of thousands of litter items gathered in the collections from both waterways.

Hard plastics were the most common items found in both rivers, followed by polystyrene in the Yarra and soft plastics in the Maribyrnong River.

The estimated quantity of rubbish has increased markedly since The Age reported the first release of statistics from the research a year ago, which showed more than 800 million pieces of trash were flowing into Port Phillip Bay from the two rivers.

Port Phillip EcoCentre marine biologist Fam Charko said protecting the bay was a responsibility shared by all Victorians.

“Port Phillip Bay is not like the ocean,” she said. “It’s a fairly enclosed marine ecosystem in the sense that it doesn’t get plastic pollution from Asia or anywhere else in the world.

“The litter we find on bay beaches is ours and ours alone.”

– Benjamin Preiss, The Age