Sewage is the most harmful form of pollution for rivers, according to a new study from the University of Oxford.
The research, published in journals Global Change Biology and Ecological Solutions, found human wastewater is “radically altering” animal, plant and microbe communities and is more damaging than agricultural waste.
It was found to be the main driver increasing algae, nutrient and sewage fungus in rivers.
Dr Dania Albini, Department of Biology, University of Oxford, and lead author of the study, 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.
“Improvements to waste water 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.”
Sewage fungus is a complex mix of fungus, algae and bacteria formed when there are high levels of organic nutrients.
It reduces oxygen levels enough to negatively affect all river species and kill a high number of fish.
At present, it has to be identified by eye - by then it is already large enough to be harmful.
Worms and cyanobacteria, known as blue-green algae, were increasingly abundant downstream of the sewage pipes, the study found.
Cyanobacteria is well known for producing toxic chemicals that can kill aquatic organisms and degrade critical ecosystems in the process.
Dr Michelle Jackson at the Department of Biology, University of Oxford, and senior author of the study, said: “There is ongoing debate about the cause of the poor ecological state of many rivers in the UK because it is difficult to disentangle different pollution sources.
“Here, we show that even treated sewage appears to have a stronger influence on river communities than pollution from the surrounding land.
“This important information should be used to prioritise the management and conservation of our rivers moving forward.
“Rapid identification of sewage fungus pollution events will allow early intervention which would help prevent any potential negative consequences for local wildlife.”
Currently, there is intense public concern over the UK’s waterways and a recent investigation discovered more than 90 per cent of England’s freshwater habitats have been degraded by farming pollution, raw sewage and water abstraction.
Agricultural run-off encouraged sensitive insect groups of mayflies, stoneflies and caddisflies, suggesting sewage is a greater threat to rivers than farming – though they added the field still needs to be kept in check.
James Wallace, the chief executive 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.
He added: “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?”