English water companies have collectively been given the lowest environmental rating by the Environment Agency (EA) since records began.
Companies were ranked on a scale of one to four stars. Out of a maximum score of 36 stars for all nine companies, the firms together scored 19, the lowest since the EA began monitoring.
The only utility to receive the highest four-star rank was Severn Trent, the agency said in its annual performance assessment.
The number of serious incidents, in which “significant” environmental harm was caused, increased by 60% last year compared to 2023.
Just three companies were responsible for the vast majority of incidents.
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Thames Water – the country’s biggest supplier – Southern Water and Yorkshire Water were responsible for 81% of all incidents.
Only two firms out of nine – Northumbrian Water and Wessex Water – recorded no serious incidents.
More monitoring, inspections and data have meant that knowledge of pollution in English waterways is now greater than ever. In turn, the amount of reporting has been greater.
Other factors driving the figures are underinvestment and poor maintenance of infrastructure, as well as wet and stormy weather.
Firms have again been called on by the Environment Agency to “urgently” improve their performance. There had previously been a trend of improvement since records began in 2011, but the latest figures indicated a “dip”.
In addition to pollution incidents, companies were assessed on self-reporting and compliance with permits.
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Is Thames Water a step closer to nationalisation?
A separate report by water regulator Ofwat published on Thursday showed “mixed” performance with improvements in sewer flooding and pipe leakage, but only two companies reported a reduction in pollution incidents over five years.
Regulation of the sector has been criticised in a once-in-a-generation review of the water industry by career civil servant Sir Jon Cunliffe. In the wake of it, the government says Ofwat is to be retired.
Pressure has mounted on utilities across the UK as the public has sought action on poor water quality and rising bills.
Thames Water, in particular, is struggling under a £20bn debt pile with the government lining up insolvency practitioners.
