Project background

Water pollution from agricultural sources, particularly Metaldedyhe, is a key issue in the Loddon catchment, which is upstream of a number of Affinity Water’s surface water abstractions from the River Thames.

Affinity Water commissioned ADAS to undertake desk-based and walkover surveys to improve knowledge of land use adjacent to the watercourse and to identify potential diffuse and point sources of pollution.


Actions taken

Information on the agronomists and contractors working in the catchment was collated and mapped, and farmers were asked a series of questions to verify metaldehyde and other oil seed rape herbicide use.

Following desk studies and postal communication with landowners, ADAS consultants produced an interactive PDF map (i-PDF) for each catchment, based on the refined surface water component of the UKWIR Intrinsic Pesticide Risk Map for metaldehyde and mobile pesticides.

A wet weather walkover survey of 4,372 ha was carried out to identify land use adjacent to the watercourse and potential diffuse and point sources of pollution (‘hotspots’). Following the survey, 76 hotspots and 25 features were identified. Each hotspot was categorised for scale and severity of the issue. Photographic evidence was also collected.

A GIS layer with colour coding by crop type, as well as locations of pollutant hotspots and ‘other features’, was produced based on the catchment walkover results.


The aim was to increase Affinity Water’s understanding of the Loddon catchment through investigations of agricultural pollution pathways, in order to support future catchment management activities and interventions. ADAS were able to identify potential agricultural pollution pathways and make recommendations for the future management of the Loddon catchment.

On completion of the catchment understanding, it was recommended that further investigations at farm and field level would be required in order to fully understand metaldehyde and OSR herbicide use.

Contact for more information

To learn more, contact Julia Dimbleby, or visit our Field, Farm and Catchment Management webpage.