New research has found that water firms are causing high levels of microplastic contamination in rivers.

Researchers at the University of Manchester found that water companies are doing a poor job of treating wastewater and raw sewage, leading to high levels of microplastic contamination.

Prof Jamie Woodward, who led the research, said: “Water companies must stop releasing untreated sewage and wastewater into rivers during periods of dry weather, as this causes riverbeds to be heavily contaminated with microplastics and maximises habitat damage.”

“Rivers are also the main supplier of microplastics to the oceans – to tackle the global marine microplastic problem, we need to limit their input to rivers.”

Data from the Environment Agency found that water companies in the UK found that discharged untreated wastewater into rivers and coastal waters over 400,000 times last year, which was for over 3.1 million hours.

In the research, which was published on Thursday in the journal Nature Sustainability, it said:

“The hotspots of microplastic contamination we have described provide unambiguous evidence that untreated wastewaters laced with raw sewage and microplastics are routinely discharged into river flows that are incapable of dispersing them downstream,” said the research.

“The discharge of raw sewage is already controversial – we have shown that the discharge of untreated effluent is the dominant pathway for the diffusion of microplastics to the heart of the riverine ecosystem.”

“Preventing deliberate ‘dry weather’ spills must be a key priority of wastewater management and environmental regulation,” the report said. “Treating these wastewaters would effectively shut down the major supply of microplastic fragments and microbeads … to riverine ecosystems and thus prevent their downstream transport to the ocean.”