Two companies are to pay thousands of pounds in compensation to a Norfolk charity after admitting their roles in polluting a river and causing the death of local wildlife.

The multinational company Lamb Weston and Ralph Harrison & Co Ltd, agreed to pay a total of £28,100 to Norfolk Rivers Trust after it was revealed that they were responsible for the pollution of the River Stiffkey at Little Snoring, near Fakenham.

The Environment Agency launched an investigation into the incident at the end of 2015 and found the pollution had been caused by rotting potatoes stored in a warehouse at Little Snoring Airfield.

The warehouse had been rented by Lamb Weston and the land was owned by Ralph Harrison & Co.

As the potatoes decomposed they released liquid that entered surface water drains and passed into a stream connected to the River Stiffkey. The liquid contained nutrients which reduced the dissolved oxygen in the stream and caused the death of fish and invertebrates within a 1km stretch of water.

Environment Agency officers found the cause was negligence on the part of Ralph Harrison & Co as no written lease agreement was in place between the two companies and no risk assessment had been prepared.

The agency opted to deal with the matter through a process known as enforcement undertakings, which allows the companies to restore and remediate any environmental damage they have caused.

Lamb Weston offered to donate £23,100 to the Norfolk Rivers Trust for use in its projects around the River Stiffkey, while Ralph Harrison & Co offered to donate £5,000 to the same charity.

Marcus Sibley, Norfolk environment manager at the Environment Agency, said: “Enforcement undertakings allow those who commit offences to restore the environment and to take steps to prevent a recurrence.

“When appropriate, they allow a quicker resolution than a prosecution and help offenders who are prepared to take responsibility for their actions to put things right voluntarily working with their local communities.”

Lamb Weston has now employed a consultant to carry out an ecological survey, created a template emergency action plan, improved staff training and employed a new storage manager.

The company also reimbursed Ralph Harrison & Co’s clean-up costs of £26,476.

Ralph Harrison & Co has dredged the stream to remove remaining pollution and installed new valve and pump systems at the site to prevent any future incidents.