was adopted as a Site of Nature Conservation Interest (SNCI) in 2009, and was restored after quarrying stopped. Beyond, the river sweeps a large curve to head northwards, and is joined by the A331, which follows the valley until past most of the conurbation. From its source up until the three-county tripoint east of Blackwater station, the river almost exactly marks the longstanding boundary between the counties of Surrey and Hampshire. On the left bank is Aldershot sewage treatment works that in dry weather supplies more than half of the local flow opposite is Willow Park Fishery. The river passes under an aqueduct carrying the Basingstoke Canal, and is then bordered by Lakeside Nature Reserve to the east and Gold Valley Lakes fishery to the west. The A331 road makes the first of the crossings. Further north is Hollybush Park, an ex-sand quarry and deep-set landfill, now an attractive grassland with wild flowers. The lakes to the north were the subject of a Planning Enquiry in 2020, to build 21 floating holiday homes and an equestrian centre. The tree-lined river path is hemmed in by railways, roads, and small lakes and is crossed by the railway line to Farnborough station, continuing north close to the A331, until it reaches junction 4 on the M3 motorway. After the M3 junction, the river is joined by Cove Brook, which starts as a series of streams near Farnborough Airport and flows northwards. For much of its route it is bordered by housing on both sides, but then passes beneath the North Downs railway line to reach the junction. The tree-lined section immediately afterwards was once a gas works and railway sidings, but is now known as Blackwater Park, as far as the A30 road bridge. The small town of Blackwater is on the left bank and Camberley sewage treatment works is on the right bank at York Town. This was the cause of a serious pollution incident in 2012, when a malfunction resulted in partially treated effluent released, contaminating the river for downstream. This resulted in fish in the Shepherds Meadow SSSI suffocating and dying. Thames Water upgraded the works after the incident. To the north of the bridge, the river is joined by the Wish Stream demarcating Surrey and Berkshire. This rises at Wishmoor Cross, in a danger area with restricted access, and flows to the south west along Wishmoor Bottom, a