Following a pollution incident in south-east London which saw the escape of sewage from a blocked sewer in 2013, Thames Water will give £80,000 to the South East Rivers Trust to make improvements to a local river.

It will also pay the Environment Agency’s full costs for the investigation of almost £20,000.

In October 2013, an underground sewer pipe in Chislehurst became lodged with tree roots, fat, oil, grease and other debris. The build-up forced sewage above ground, flooding a field and two streams, before entering the River Shuttle.

Officers from the Environment Agency believe the sewage, which killed as many as 20 stickleback fish and hundreds of invertebrates, could have been flowing for several days. The effect of the pollution on water quality and river habitats was seen over several miles.

Following the Environment Agency’s investigation, Thames Water installed equipment to monitor sewage levels in its sewer network, near to where the blockage occurred. This will tell them about any developing problems, and allow obstructions to be cleared as soon as possible. The company has also relined the sewer to help prevent roots entering the pipes again.

Thames Water will make the £80,000 payment as a civil sanction, also known as an enforcement undertaking. Companies and individuals can make good some of the environmental damage they cause, including through a financial contribution to a local project. The Environment Agency must also be satisfied the polluter will make changes to its operations to prevent similar damage in the future.

The South East Rivers Trust, which helps communities look after rivers, will use the money to install a fish pass on the River Cray at Bexley, allowing various types of fish to swim upstream, beyond an historic weir at Hall Place, to the upper reaches of the river.