Canvey Island is a town, civil parish and reclaimed island in the Thames estuary, near Southend-on-Sea, in the Castle Point district, in the county of Essex, England. It has an area of 7.12 square miles (18.44 km2) and a population of 38,170. It is separated from the mainland of south Essex by a network of creeks. Lying only just above sea level, it is prone to flooding at exceptional tides and has been inhabited since the Roman conquest of Britain.
The island was mainly agricultural land until the 20th century, when it became the fastest-growing seaside resort in Britain between 1911 and 1951. The North Sea flood of 1953 devastated the island, killing 58 islanders and leading to the temporary evacuation of the 13,000 residents. Canvey is consequently protected by modern sea defences comprising 2 miles (3.2 km) of concrete sea walls.
Canvey Island is also notable for its relationship to the petrochemical industry. The island was the site of the first delivery in the world of liquefied natural gas by container ship and later became the subject of an influential assessment on the risks to a population living within the vicinity of petrochemical shipping and storage facilities.