'The Blackwater Valley is maintained as an open space along the borders of the English counties of Berkshire, Hampshire and Surrey. It runs for approximately 30 km, from the source of the River Blackwater at Rowhill Nature Reserve near Aldershot in the south, northwards to Swallowfield where the river joins the River Whitewater and then the Loddon. The Loddon eventually flows into the River Thames near Reading.'