Its main importance lies in its extensive diversity of birdlife in lakes in former gravel pits .
Mid Colne Valley is a 132 hectare biological Site of Special Scientific Interest in Harefield in the London Borough of Hillingdon and Denham in South Buckinghamshire .
Mid Colne Valley 's main importance lies in its extensive diversity of birdlife in lakes in former gravel pits .
Mid Colne Valley is a 132 hectare biological Site of Special Scientific Interest in Harefield in the London Borough of Hillingdon and Denham in South Buckinghamshire .