Public Information Notice: Blue-Green Algae Bloom in the River Thames

Dear Residents.

Please be advised that the Environment Agency has detected a blue-green algae bloom in the River Thames. The incident was first identified on the 18 August 2026 and remains under ongoing assessment and monitoring. The bloom continues to persist along a 10-kilometre stretch of the lower River Thames, between Sunbury Lock and Teddington Lock, including the Ham and Kingston Designated Bathing Water area.

This has been classified as a Category 1 environmental incident due to the potential risks it poses to:

There also have been unconfirmed sightings of small, isolated patches of algae within the tidal Thames between Teddington Lock and Richmond Half Tide Lock (approximately 5 kilometres). While conditions in the tidal Thames are generally less favourable for this type of algae due to salinity, turbidity, and tidal water movement, there remains a possibility that patches could spread with tidal activity.

As a precaution, members of the public are advised to exercise increased caution in the upper tidal Thames:

At present, it is not possible to predict how long the algae bloom will persist. However, cooler weather conditions and increased river flows are expected to help improve the situation over time.

Please report environmental incidents, including

         Fish in distress

        Suspected algae blooms in other areas of the river

Any related environmental concerns on: report environmental incidents on GOV.UK or by calling the Environmental Agency incident hotline: 0800 807060

Further updates will be provided as the situation develops. 

For official guidance, please visit: algal blooms: advice for the public and landowners - GOV.UK  

Thank you for your co-operation and support.