Pollution from treated and untreated sewage is the greatest threat to river biodiversity, causing more damage than runoff from farms, according to research.
There is a need for more regulation of water companies and improvements at their treatment plans to protect rivers, say the authors of the study.
The research from the University of Oxford was released on World Rivers Day. No river in England passes tests for chemical or biological pollution, and government targets to improve the water quality in rivers will not be met.
“Improvements to wastewater plants should be implemented along with more regulations. These efforts are crucial in safeguarding the integrity and safety of our rivers – fundamental elements of both ecosystems and human wellbeing,” said the lead author, Dr Dania Albini, of Oxford’s biology department.
Treated sewage released by water companies into rivers and raw effluent that is dumped in rivers via storm overflows is the primary driver of increased nutrients, algae and sewage fungus in rivers, according to the study.
Sewage discharge radically alters plant, animal and microbe communities and increases the abundance of harmful species. While runoff from farmland has negative impacts on river water quality, the research reveals that sewage discharge into rivers has a greater impact on water quality and the animals and plants that live in rivers.
The findings were published in the journals Global Change Biology and Ecological Solutions and Evidence.
Albini said: “Our study highlights the disproportionate impact that sewage discharge has on river quality, presenting an urgent need for a comprehensive action plan targeting the sewage discharge problem.”
Sewage from households and businesses is treated by water companies at treatment plants and then discharged into rivers. Raw sewage is also discharged via storm overflows, but this should only take place in exceptional circumstances. Water companies are at the centre of a criminal investigation by the Environment Agency and an inquiry by the financial regulator Ofwat into failures in the way they run their treatment plants.
James Wallace, of the UK-based charity River Action, said: “This important research demonstrates yet again the damage from unregulated water companies and agriculture. In addition to the catastrophic impact on wildlife from nutrient pollution, the public should be aware that sewage systems do not remove dangerous bacteria such as E.coli and intestinal enterococci from treated sewage.
“When will the government make water companies and farms clean up their act, especially in places where human lives and sensitive protected habitats are threatened?”
Separate research by Dr Leon Barron, part of the Environmental Research Group at Imperial College, which involved hundreds of samples taken from 14 waterways in Greater London over three years, reveals that 21 compounds were detected that posed a potential risk to the environment in freshwater ecosystems. The pollutants included antibiotics, pain medication and pet parasite medications, which contain neonicotinoids.
The study showed that water companies’ treatment plants and combined sewer overflows, which release raw sewage and runoff, were the main sources of chemical risks to rivers overall.
The team found that smaller rivers feeding into the Thames were most affected by wastewater pollution.
The research compared sampling taken during Covid lockdowns with those taken when society opened up again. Barron, a senior author of the research, said it was the largest study of a heavily urbanised river system and provided uniquely detailed insights into London’s water quality.
Guy Woodward, a professor of ecology in the department of life sciences at Imperial, and a co-author of the paper, said: “This … picks up on several [chemicals] that are at potentially harmful concentrations for wildlife, but which have seemingly been overlooked in traditional surveys of our water quality in urban areas at this resolution.”
