Wessex Water has made a £278,000 payment under an Enforcement Undertaking following a serious pollution incident in the River Sheppey in August 2019, which killed around 8,000 fish and caused significant ecological damage.

The Environment Agency confirmed it had accepted the voluntary settlement as a way of addressing the harm caused by the incident, which was categorised as Category 1 — the most severe classification for environmental harm.

The agreement includes:

• A £103,000 contribution to the Farming and Wildlife Advisory Group South West (FWAGSW)
• £175,000 invested in real-time water quality monitoring for the catchment and Shepton Mallet treatment site
• A compensation payment to a third party
• Full reimbursement of the Environment Agency's investigation costs

The details came to light following a Freedom of Information (FOI) request submitted earlier this year.

Cause of the pollution

The pollution followed an unauthorised discharge by a third party into the public sewer, which overwhelmed treatment processes at Wessex Water's Shepton Mallet Water Recycling Centre. The resulting failure led to the site breaching its permit for biochemical oxygen demand (BOD) and iron.

Routine testing on 31 July 2019 identified an unknown substance with high chemical oxygen demand (COD) entering the site. The breach caused serious harm to the river's fish and invertebrate populations across a 15km stretch between Shepton Mallet, Wells, and Meare.

The site returned to compliance by 9 August, but the pollution had already taken effect.

In a statement issued this week, a Wessex Water spokesperson said: "An unauthorised discharge by a third party into the public sewer caused a breakdown of treatment processes at our water recycling centre and led to the death of a significant number of fish in the River Sheppey, a deeply regrettable event.

Wessex Water has worked closely with the third party in question to improve their on-site activities. The Enforcement Undertaking includes a commitment to install equipment that will monitor discharges from traders in the sewer catchment, providing an early warning to help prevent future pollutions."

What is an Enforcement Undertaking?

An Enforcement Undertaking is a voluntary agreement between a company and the Environment Agency, used as an alternative to prosecution. It must include steps to put right or mitigate environmental harm and is only accepted where the Agency considers it appropriate.

In this case, the Agency said it had chosen to accept the undertaking "as a means of helping to address the harm caused by the incident." It has not announced any further enforcement action.

In the days following the spill, emergency aeration devices were used in the River Sheppey to increase oxygen levels and reduce the impact on surviving aquatic life. Local residents described seeing "hundreds" of dead fish, with the ecosystem left severely disrupted.

The full FOI response is available here.