Southfield Farm Marsh is an 8.6-hectare (21-acre) biological Site of Special Scientific Interest in Kettering in Northamptonshire.

[1][2] An area of 2.8 hectares is managed as a nature reserve by the Wildlife Trust for Bedfordshire, Cambridgeshire and Northamptonshire.

[3] The wetland has tall plants such as lesser pond-sedge and slender tufted-sedge, which provides cover for reed buntings and sedge warblers.

Mammals include otters, and there are birds such as red kites and buzzards.

Purple loosestrife is found in grassland areas.