Clean up operations by agencies yield 11.3 tonnes of rubbish from Perth waterways and foreshores. More than 6 tonnes from the Swan and Canning Rivers were trash and 5 tonnes were timber and rubble from two days of clean up.

Among the most common type of trash thrown into the waterways were tyres which the Swan River Trust retrieved 48 pieces in the last 12 months. However, there was a significant decline in the number of shopping trolleys recovered at only 9 compared to 48 the previous year.

On the rise were vandalised signs, including real estate and street signs which increased to 19 from 10, and drums which more than doubled to 16 from 7.

"Most disturbing is the mass of plastic bags and fishing line that continues to be found, despite people knowing the terrible impacts these items have on river wildlife from pelicans to dolphins, Western Australia Environment Minister Bill Marmion said in a statement.

"One of the more damaging things is fishing lines that can get tangled up in fish and we just had the situation about six months ago with the dolphin Gizmo which had fishing line entangled in its finds and it cut about a third into its fins," he added.

The volume of trash thrown into the state's waterways kept on increasing despite the state hiking fines for illegal dumping and littering. According to Australia's litter index, Western Australians are among the worst litterers in the country, confirmed by the garbage yield from the two rivers, Mr Marmion said.

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