Polystyrene, food wrappers and cigarette butts were among the most common items found by volunteers collecting rubbish from Australia's largest waterways.
They picked up more than a quarter of a million pieces of trash in the past 18 months but there's still a lot more work to be done, Conservation Volunteers Australia says.
The group is calling on everyday people, businesses and politicians to volunteer on April 23 for a national day of collecting litter.
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"Australia ranks number one in the world for its coastal, nature and wildlife tourism and, with global borders reopening after two years, it is doubly critical for environmental and economic recovery we all lend a hand," chief executive Phil Harrison said on Monday.
"It's critical for the nation's environmental and economic recovery that Australia's world-famous riverbanks, bays and beaches are dressed for success."
A CSIRO study found it takes as few as 14 pieces of plastic to kill a sea turtle. The science agency predicts 99 per cent of sea birds will have ingested plastic by 2050, while others suggest there will be more plastic in the ocean than fish by the same date.
"Once small plastics like polystyrene enter the water, they're both a major threat to wildlife and food chains, and near on impossible to remove," Mr Harrison said.
"Many people also don't realise cigarette butts are considered plastic waste, not paper, and therefore don't break down, ensuring they remain a major threat to marine wildlife health."
The federal government released its national plastics plan in 2021, declaring it would take the fight against plastic waste to a new level.
It promised an end to the confusion over household collection systems, plastic-free beaches, a war on cigarette butts and a ban on polystyrene packaging.
The Sea To Source program, which is sponsored by the federal government, focuses on eight key river systems across the county.
More than 3000 volunteers helped remove trash from the Parramatta, Georges, Brisbane, Werribee, Torrens, Swan, Derwent and Tamar rivers in the past 18 months.
Australian Associated Press