River Mersey faces 'extreme' sewage pollution as researchers warn 'immediate action' is needed

The Mersey Estuary is facing ‘extreme’ levels of sewage pollution, despite efforts to clean up the river once dubbed the most polluted in Western Europe.

Researchers at Durham University used seaweed to examine nitrogen pollution in the Estuary and say the shock findings could mean that many other rivers and estuaries in the UK are far more polluted than currently believed.

The study, published in the journal Environmental Science: Advances, saw researchers used herbaria (dried seaweed) from the collection at the World Museum in Liverpool to investigate nitrogen pollution in the Mersey Estuary over the past 200-years.   

The Durham team analysed small parts of the herbaria collected from the the River Mersey and Liverpool Docks from 1821 to 2022 and used the nitrogen isotope data to identify historical changes in industrial and/or sewage pollution. Dr Geraldine Reid, Lead Curator of Botany, Geology & Science at National Museums Liverpool said: "Herbaria are a globally scientific resource that are under-utilised as a tool for tracking historical changes in our environment. Herbaria act like time capsules, capturing in its tissues the environmental conditions it was growing in.”

Last year, the results of the first survey of its kind in two decades showed a huge increase in fish populations, suggesting the Mersey was finally recovering from industrial pollution and sewage. The research by the Mersey Rivers Trust found the number of different kinds of fish in the estuary had more than doubled. However, Durham University’s new research suggests that sewage pollution in the Mersey Estuary is increasing to levels only last seen in the record from the 1980s, when a public outcry sparked a major clean-up campaign.

Professor Darren Gröcke of Durham University explained: “We found that the Mersey Estuary herbaria and modern seaweed samples record some of the highest nitrogen isotope values ever recorded in macroalgae.

“When we generated the nitrogen data from our modern survey, which involved us collecting seaweed in 2022, it surprised us as we were not expecting such extreme values. This tells us that there is still a lot of sewage effluent going into the River Mersey. “This study shows the devastating state and impact of sewage pollution in the UK, which requires immediate action.”

The researchers suggest the data represents an ongoing failure to improve the UK’s water quality by reducing sewage discharges into our waterways.   

Professor Gröcke continued: “The rise in nitrogen levels in the Mersey Estuary correspond not only with the development of sewage treatment plants, but also by the privatisation of those plants, and it seems that we are reverting to sewage nitrogen pollution issues last seen in the 1980s.

“Our research clearly shows that the Mersey Estuary is suffering dramatically from sewage nitrogen pollution. Further investigation of other UK estuaries may show that the environmental situation in the Mersey Estuary is not unique. Basically, we need action to clean up our rivers, because this isn't just a River Mersey problem; it is a UK-wide problem.”