Brentford Lock Water Tests Cause Concern

Local Green party took measurements as part of national initiative

Volunteers testing the water near Brentford Lock. Picture: Hounslow Green Party

May 9, 2025

Members of the Hounslow Green Party are raising concerns about the levels of pollutants they have found during test around Brentford Lock.

They have participated in three main testing regimes recently including those conducted by the Rivers Trust as part of the Big River Watch, the Fresh Water Watch (testing for Nitrogen and phosphates) and the Clean Up River Brent Campaign, with Imperial College.

The four volunteers who tested the water at Brentford Lock and in nearby waterways found nitrogen levels at Moderate or High and phosphates were found to be High, which they believe could indicate runoffs from fertiliser. These high levels may explain the poor ecological status, and the decline in wildlife, observed in the Big River Watch.

Investigations by local environmental groups including Clean Up the River Brent campaign (CURB) and Friends of the River Crane have used Freedom of Information requests to identify an issue with misconnected sewers pumping foul water into local sewers. The water around Brentford Lock will be affected by discharges into the River Brent.

The UK Great Water Blitz reported back last September and concluded that 61% of data points across the UK showed poor water quality with significant regional variation the Anglian and Thames river basin districts have the worst water quality in the UK: over 80% of surveys showed unacceptable nutrient concentrations.

For this study , Earthwatch partnered with Imperial College London to undertake additional chemical analysis of a selection of water samples. In addition to its nutrient testing, community groups, such as the one in Brentford, collected water samples which were analysed by Dr Leon Barron and his team in the labs at Imperial.

Although the opening of the Tideway Tunnel is expected to significantly increase water quality in the Thames, all of the storm discharge points which are no longer expected to see regular outflows are down river from Brentford. Meanwhile the sewage treatment plant at Mogden continues to discharge into the river and, although this water has been treated, it still does contain pollutants.