from the aquifers, but by far the largest component of the flow is the discharge from five major sewage treatment works on the upper reaches and two smaller ones on the lower reaches. The springs are quite acidic for natural, non-hydrothermal springs. After flowing over the London clay deposits, the underlying geology is more permeable near the mouth, the "Bagshot and Bracklesham" Sands. In 1992, the five works could discharge up to 74.4 Ml per day, and in summer months accounted for around 85% of flow above the confluence with the Whitewater. The valley has large pockets of deep gravels, quarried since the 1950s. This explains the many lakes in the valley, as old workings (pits) fill with water. Many have been landscaped as park lakes and used for fishing and sailing. A number of them are designated Sites of Special Scientific Interest (SSSI), having rich and diverse ecology. The Blackwater Valley SSSI covers , comprising unimproved alluvial meadows, swamp, and wet woodland. Part of it is managed by the Berkshire, Buckinghamshire and Oxfordshire Naturalists Trust. The rest is managed by Bracknell Forest Council, Shepherd Meadows. The river is crossed by a small part of the Basingstoke Canal SSSI, which supports the widest variety of aquatic species in England. The Valley is the key verdant buffer zone and park amenity for local residents. As well as the SSSIs, there are three nature reserves. Much of the rest of the drainage basin not built upon is ecologically important. Thirty-one 'Wildlife Sites' have been designated by the local planning authorities and a riverside path has opened up much of the riverbank. A large running club in local ranks use the path regularly. From an improvement programme, wildlife is returning, including the otter which has been absent for over 40 years, and fish stocks are improving. A cycle route runs alongside the river for most of its length. Route The Blackwater rises as a series of springs on Rowhill Copse, a nature reserve to the south-west of Aldershot. The site contains a range of habitats, its estate once produced timber and bricks. The river curves east-south-east, passing under the railway line to station, between two lakes, under Badshot Lea Road and past some more lakes, which form part of Tice's Meadow nature reserve, a hop farm from 1851 until 1958, after which were quarried by Hanson Aggregates between 1998 and 2010. The site