Horsea Island was an island located off the northern shore of Portsmouth Harbour, England; gradually subsumed by reclamation, it is now connected to the mainland. Horsea falls within the city of Portsmouth and was wholly owned by the Ministry of Defence as part of the shore establishment HMS Excellent, which maintains its headquarters on Whale Island.
However, in 2013 the south-eastern corner was acquired by Portsmouth City Council for housing development.[1] Most of the area to the south-west of the lake is part of the Portsmouth Harbour Site of Special Scientific Interest (SSSI), the remainder was declared a Site of Importance for Nature Conservation (SINC) in 2011.