United Utilities fined after valve test triggers mass fish deaths

United Utilities has been fined £60,000 after a routine reservoir test led to the deaths of more than 16,000 fish in a brook near Bolton—marking a first-of-its-kind prosecution for the water industry.

The incident occurred during a valve test at High Rid Reservoir, when more than 30,000 fish were unexpectedly released into Bessy Brook. The narrow watercourse proved unable to support such a large number, leaving thousands dead or severely injured.

Investigators described distressing scenes, with fish found embedded in bridge walls and others showing clear signs of trauma. While around 18,000 fish were eventually rescued and returned to the reservoir, the scale of the loss was significant.

Following an Environment Agency investigation, the company admitted it had failed to obtain the required permit to release fish into inland waters. The case is the first time a water company has been sentenced under the 2015 regulations governing fish introduction.

Officials confirmed the incident caused a “significant adverse impact” on animal health, despite there being no evidence of pollution in the water.

United Utilities said the event may have been triggered by fish entering pipework to escape predators, and told the court it has since taken steps to prevent a repeat. The company has also made a voluntary £500,000 donation towards local environmental restoration.

Regulators, however, were clear: compliance is non-negotiable. The Environment Agency said the prosecution sends a strong signal to water companies that breaches will be met with firm action.

Water Minister Emma Hardy described the incident as “shocking,” adding that tougher oversight of the sector is on the way to prevent similar failures in the future.