A new technique for tracking down the source of river pollutants has been developed by researchers from the University of Oxford.

The computational method, created in collaboration with Imperial College London, uses an innovative approach to identify the origins of harmful substances in rivers.

In a case study, the model successfully pinpointed the source of a banned neonicotinoid pesticide in a rare chalk stream habitat.

Currently, only 14 per cent of rivers in England meet the 'good' ecological status due to pollution from sewage and agricultural chemicals.

Until now, there has not been a reliable method to identify the sources of river pollution, making it almost impossible to address the problem effectively.

The study introduces a new approach using 'inverse modelling', which traces pollution in rivers back to its likely source.

This contrasts with current 'forward modelling' methods that start with assumed pollution sources and estimate their eventual distribution.

The study's co-lead, Dr Alex Lipp, from Oxford University, said: "The first step to mitigating a polluted river is working out where the problem is.

"These new mathematical 'inverse' methods provide an objective way to determine where and how pollutants enter river networks from monitoring data alone."

The new technique was tested on the River Wandle, a chalk stream in southwest London which has prompted local outrage over recent sewage dumping.

The researchers found the banned pesticide imidacloprid was entering the river from a section containing the outflow of a sewage treatment plant.

Co-lead author, Dr Gareth Roberts, from Imperial College London, said: "This supports the idea that imidacloprid in our rivers can originate from its use as pet medication, entering sewage systems after being washed down drains and evading removal at wastewater treatment facilities."

Dr Lipp hopes to see the inverse-modelling approach scaled up and incorporated into future water quality monitoring.

He said: "One application of this approach I’m very interested in is the analysis of citizen science data.

"Citizen campaign groups are now frequently generating fantastic high-density datasets of pollutants such as phosphorus and nitrate in rivers, and this inverse approach could be used to turn this data into actionable insights."

The model is based on public data released by Thames Water on sewage discharges.

Currently, it cannot be scaled up to the rest of the UK as no other water companies make this information accessible.

Dr Lipp said: "This is why it is so important that water companies follow the lead of Thames Water, releasing environmental data in an accessible format for the public, and scientists, to use."