Testing of rivers in England has fallen dramatically in the past 10 years, with experts warning it leaves a vacuum of knowledge about the effects of pollution.

Environment Agency data shows its river testing has fallen from nearly 100,000 samples a year in 2012 to 41,519 in 2021 – the lowest level of sampling in 20 years apart from the drop-off during Covid in 2020.

The dramatic fall in monitoring coincides with repeated cuts to the EA budget, in what its outgoing chair, Emma Howard Boyd, said had stopped the agency from carrying out vital water quality work.

Dr Barnaby Dobson, an expert in water systems from Imperial College London, said: “If you ask what are the biggest risks to water quality, my view is that it is the lack of sampling and monitoring. We cannot work out where we are failing if we are not looking.

“We cannot know about the impact on rivers if we are not sampling any of them. How can we know what the biggest water quality threats that the country faces are if we are not looking in rivers?”

The risk of pollution increases when rivers are at low flow during drought conditions, as they have been this year. The last tests carried out under the EU water framework directive in 2019 showed English rivers were in a shocking state, with no river passing quality tests for ecological and chemical status.

Dobson said in a paper published this month on testing of river catchments that informal testing schemes were increasingly supplanting routine regulatory surveys, such as those of the EA, for river sampling. He said funding for sampling needed to be restored to the EA.

According to recent data, the main reasons for rivers failing to pass ecological and chemical quality tests are pollution from sewage discharges, treated and untreated, and agricultural runoff. Agriculture affects nearly two-thirds of rivers, the water sector affects more than half, and the urban and transport sector a quarter.

The report found the single activity with the most widespread impact on rivers was discharges of treated sewage effluent, which affected 43% of river water bodies in 2020. The effects of raw sewage spills via storm overflows contributed towards 12% of river water bodies failing standards.

An Environment Agency spokesperson said: “We continue to take tens of thousands of water quality samples every year as part of our work to keep rivers clean. In recent years technological advances and increased efficiency has enabled us to concentrate our resources, and target areas where the environment will benefit most.”

The full story in the Guardian can be read here.