THE Boxing Day floods in 2015 almost emptied some of Bolton's rivers of microbead pollutants by washing them towards the sea.

A study carried out by the University of Manchester looked at the levels of microplastics in Greater Manchester's rivers before and after the Boxing Day flooding.

Of the five sites tested in Bolton all but one saw a decrease in microplastic pollution and the River Tonge saw a decrease of 94 per cent.

Professor Jamie Woodward, the university's head of geography, said: "Microplastics in the ocean have recently attracted a lot of attention, but until now science knew little about the major sources of this pollution and the transport processes involved.

"We decided to explore the contamination of urban river beds, as we began to think that they may be the main source of the problem."

Researchers studied rural streams and urban rivers at 40 sites across Greater Manchester, and discovered tiny plastic beads, fibres and fragments in all parts of the network.

Microplastics, which come from a variety of sources including clothing and cosmetics, can be harmful to marine life and pose a threat to ecosystem health.

The scientists are calling for tighter regulations on waste flowing into urban waterways, and say pollution in these channels is a "major contributor" to contamination in the oceans.

Prior to the flooding, when it was tested between April and July 2015, the River Tonge at Waters Meeting Road had the third highest levels of microplastics at 26,800 particles per sq m.

When tested after the flooding between May and July 2016, there were 1,500 particles per sq m.

Tests at Nob End showed a drop of 84 per cent and where the rivers Irwell and Croal meet a drop of 79 per cent. Tests in Darcy Lever showed a lesser drop of 33 per cent.

Egerton was the only site in Bolton which showed an increase. The waterway tested in Egerton increased from 500 particles per sq m to 600, a rise of 20 per cent.

Across Greater Manchester the researchers saw a 70 per cent drop in the microplastics on the riverbed — equivalent to about 40 billion particles — suggesting large quantities had been flushed into the ocean.

Prof Woodward added: "We are only beginning to understand the extent of the microplastic contamination problem in the world's rivers.

"To tackle the problem in the oceans, we have to prevent microplastics entering river channels.

"We also need to reduce our use of plastics large and small."

Earlier this year, a UK-wide ban on adding microbeads into rinse-off cosmetics and personal care products such as face scrubs, toothpastes and shower gels came into force.