Tipner Lake forms the north eastern section of Portsmouth Harbour. It is not an actual lake, but the reclamation of land north of Horsea Island  and the building of the M275 motorway in the early 1970s, which passes over a bridge to the west of the lake, can give the impression the body of water is no longer connected to the harbour. The lake is also connected to Portsbridge Creek, the site also falls within the Portsmouth Harbour special protection area.