'We've seen a huge deterioration in the performance of Dŵr Cymru Welsh Water since 2020...'

Dwr Cymru in England and Wales has generally increased.

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“In 2024, the company experienced the highest number of sewage pollution incidents since 2015, as well as the second-highest overall total of pollution incidents during this period?

‘There were six pollution incidents listed as “serious” by the regulator in 2024, down one on the year before, but double the 2021 figure.

‘The report also lists the number of pollution incidents caused solely by Dwr Cymru's sewerage assets.

Between 2015 and 2020, pollution incidents per unit of sewer length decreased, but have risen each year over the past four years, reaching a ten-year high of 36 incidents per 10,000 km of sewer in 2024.

‘The top source of pollution from assets owned by Dwr Cymru was foul sewers, far in excess of the other things in the top five - combined sewer overflows, water treatment works, pumping stations, and the water distribution system.

‘The report also looks at the performance of Hafren Dyfrdwy, which also operates in Wales. Over the past decade, pollution incidents from Hafren Dyfrdwy’s sewerage and water assets have generally declined, with a brief rise in 2020-21 before falling again in the last three years.

Pollution incidents caused solely by Hafren Dyfrdwy's sewerage assets doubled in 2024 from 20 in 2023.

Pollution incidents come from various assets, with the top causes over the last 10 years being the water distribution system, combined sewer overflows and foul sewers.

NRW says it can take action from giving advice right through to prosecution in the courts, but it does warn in the report that complex investigations can take years.

Since 2015, the regulator says, it has issued four notices, 24 formal cautions and 10 prosecutions.