The Blackwater Valley is located on the borders of Hampshire, Surrey and Berkshire and runs for approximately 30km from the source near Aldershot, northwards to Swallowfield. At its confluence it joins the rivers Whitewater and Loddon. The Loddon eventually flows into the River Thames near Reading.
Work in the Blackwater Valley is co-ordinated by the Blackwater Valley Countryside Partnership on behalf of the local authorities that border the Valley.
Despite being surrounded by urban development the Valley provides an important green corridor for local residents As well as the Blackwater Valley Site of Special Scientific Interest (SSSI) and a small part of the Basingstoke Canal SSSI, three nature reserves within the Valley catchment and many other areas have been recognised for their ecological importance. The local planning authorities covering the Valley have designated 31 other areas as ‘Wildlife Sites’.