Campaigners fear the change of approach could lead to more pollution in England’s rivers and waterways if the new measuring methods are less rigorous.

Recent analysis found that many toxic chemicals and pesticides banned in the bloc since Brexit are not outlawed for use in the UK. Ministers are also attempting to rip up EU-derived sewage pollution rules for housebuilders.

In 2019, the last time the full water assessments took place, just 14% of rivers were in good ecological health and none met standards for good chemical health.

The Guardian can reveal that the government will be using its own, as yet undisclosed methodology to assess river health. Activists say this may make it harder to compare the state of the country’s rivers against those in the EU, and will leave the public in the dark over pollution from sewage and agriculture.