Wessex Water has been fined £500,000 for polluting two rivers and killing thousands of fish.

The company admitted a series of failures which led to untreated sewage being discharged into the rivers in Wiltshire and North Somerset in 2018.

Janine Maclean, from the Environment Agency, said: “These cases are further examples of a water company breaking the law and causing serious pollution.”

It is the second-highest fine in the company’s history. A Wessex Water spokesperson apologised and said the incidents “shouldn’t have happened”.

Clackers Brook is a small river in Wiltshire. It rises near Bromham and runs just five miles into Melksham, where it joins the River Avon.

But in that first five miles, it passes the Wessex Water sewage pumping station at Bowerhill Lodge.

In April 2018 the company allowed storm water with untreated sewage to flow into the river for 54 hours.

Later the same year, there was a mechanical and electrical failure which led to more sewage flowing into Clackers Brook.

The Environment Agency found that 2,100 fish died, including eels and lampreys both endangered and protected species.

Investigators reported that all fish within 1km of the spill were killed.

Senior officer Janine Maclean said it was “very sad the pollutions had such serious impacts – killing fish and other aquatic life”.

The agency took Wessex Water to court for breaching their licence, and the company admitted the offences.

Meanwhile in North Somerset, near Weston-super-Mare, another sewage pipe burst in August 2018. Again, untreated effluent polluted the rivers and the local marsh rhyne drainage system.

This led to more fish dying, including spined stickleback and eels.

The sewage pipe in question was a so-called “rising main”, a pipe through which sewage is pumped under pressure.

The rising main had already been identified by Wessex Water prior to the incident, as a critical one that needed to be monitored, but the monitoring was not put in place until after the incident.

District Judge Joanna Dickens, sitting at Swindon Magistrates Court, ruled the company was negligent, because “of the failure to install monitoring equipment at an earlier time”.

The Environment Agency said that Wessex Water’s rising mains are “ageing” and account for many of the company’s pollution incidents.

Janine Maclean, of the Environment Agency, said: “We recognise the company is increasing its monitoring of rising mains, but monitoring is still reliant on failure, and we would like to see the company significantly increase the level of investment it makes to proactively replace rising mains before they fail.”

A Wessex Water spokesperson apologised for the incidents, and said the company had done what it could as soon it realised what had happened.

They continued: “Since these incidents took place, we have invested in AI technology to detect where potential issues on our network might occur to further protect the environment.”