Thames Water has recorded a 25 per cent rise in the most serious type of water pollution incidents this year.

Information obtained by law firm Legal Expert through Freedom of Information Requests to the Environment Agency has shown the country's biggest household supplier reported 16 category one pollution incidents, the most serious level, in 2023, which increased to 20 in 2024.

The figures emerge as Thames Water, Yorkshire Water and Northumbrian Water face fines of £168 million for historical sewage spills.

Ofwat, the industry regulator, announced the fines on July 31 amid growing public discontent over the environmental and financial performance of some major water companies.

The proposed penalty will be taken to public consultation, forming part of Ofwat's biggest ever investigation into water company performance.

Thames Water alone is facing fines of £104 million. Ofwat holds the power to fine companies up to 10 per cent of their annual sales. In this instance, the proposed fine is nine per cent of sales.

Environment Agency figures obtained by Legal Expert show the majority of England’s nine water and sewage companies have recorded 92 per cent of serious pollution incidents this year alone.

However, figures for serious water pollution incidents for Severn Trent and Northumbrian Water are incomplete for 2024.

Yorkshire Water has also recorded an increase in serious incidents this year, with 11, up from six in 2023.

Southern Water and Anglian Water saw a decrease in incidents with eight and six respectively, both down from 16 and 11 in 2023.

The Environment Agency classifies pollution incidents as serious if they are either significant (category two) or major (category one).

Such incidents might include events that pose harm to wildlife such as causing fish to die or potentially endangering bathers, as well as situations where drinking water providers are forced to halt the water supply from a river temporarily.

The data obtained by Legal Expert also shows the leading causes and pollutants contributing to serious water pollution incidents in England and Wales over the past five years.

From 2019 to 2024, the leading cause of incidents reported was 'containment and control', accounting for 83 per cent of all incidents over the last five years.

This term covers occurrences like pipeline failures that result in hazardous materials being released into the environment.

Since 2019, some 250 incidents have been recorded and in 79 per cent of these cases, crude sewage was the pollutant.