A study conducted by the University of Oxford has revealed that sewage discharge into rivers has a greater impact on water quality than agricultural land use.

The university released the paper, ‘Early detection and environmental drivers of sewage fungus outbreaks in rivers‘, ahead of World Rivers Day tomorrow (September 24).

The University of Oxford said the main threat to the UK’s rivers is the release of treated waste water into them by water companies, and untreated waste water during heavy rainfalls (storm overflow).

As well as ecological consequences, the University of Oxford said this poses “serious threats” for human wellbeing if the water is then used for drinking, recreational or agricultural purposes.


Researchers from the University of Oxford’s department of biology investigated the effects of three different pollution sources (treated sewage discharge, agriculture, and urban run-off) on different aspects of river systems.

The group tested four rivers in England, both up- and downstream of sewage discharge, over three different months.

The results demonstrated that treated sewage discharge was the best predictor of high nutrient levels, bottom-dwelling algae, and sewage fungus abundance, regardless of the type of land use (agriculture or urban) in the surrounding area.

Senior author of the study, Dr. Michelle Jackson, 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.”

Dr. Dania Albini of the University of Oxford’s department of biology, and lead author of the study, said the study highlights the “disproportionate impact” that sewage discharge has on river quality, presenting an urgent need for an action plan targeting this.

“Improvements to waste water plants should be implemented along with more regulations,” she said.

“These efforts are crucial in safeguarding the integrity and safety of our rivers — fundamental elements of both ecosystems and human wellbeing.”

Water pollution

The University of Oxford said nutrients exacerbate the decline of waterways by promoting the growth of harmful species and deteriorating others.

In terms of agricultural pollution, the university said only one measurement in its study was best predicted by agricultural land use.

This was through the abundance of the sensitive insect groups of mayflies, stoneflies, and caddisflies.

“This suggests that water quality and river communities are generally more threatened by treated sewage discharge than pollution from the surrounding catchment, but agricultural pollution also needs to be kept in check,” the university said.