Mersea Island is an island in Essex, England, in the Blackwater and Colne estuaries to the south-east of Colchester. Its name comes from the Old English word meresig, meaning "island of the pool" and thus is tautological. The island is split into two main areas, West Mersea and East Mersea, and connected to the mainland by the Strood, a causeway that can flood at high tide.
The island has been inhabited since pre-Roman times. It was used as a holiday destination in Roman Britain for occupants of Camulodunum. Fishing has been a key industry on the island since then, particularly oysters, and along with tourism makes up a significant part of the island's economy.
Coordinates 51°46'19.004" N 0°53'58.316" E