The Maplin Sands are mudflats on the northern bank of the Thames estuary, off Foulness Island, near Southend-on-Sea in Essex, England, though they actually lie within the neighbouring borough of Rochford. They are valuable as a wildlife reserve, with a large colony of dwarf eelgrass (Zostera noltei) and associated animal communities.
A screw-pile lighthouse was built on the sands in 1838, which was possibly the world's first.
In the later part of the 19th century John I. Thornycroft & Company and Yarrow Shipbuilders used the sands for their Destroyers measured mile speed trials.[1] The shallow waters resulted in a flow of water that could add up to a knot to the ship's speed.[1] When the Admiralty found out they required that all future trials be carried out in deep water.[1]
A plan to build a third airport for London on the sands was approved in 1973, but abandoned in 1974 in the wake of the 1973/74 oil crisis. The project would have included not just a major airport, but a deep-water harbour suitable for the container ships then coming into use, a high-speed rail link to London, and a new town for the accommodation of the thousands of workers who would be required. (See main article on Thames Estuary Airport.)
The Maplin Sands were at that time, and remain, a military testing ground belonging to the Ministry of Defence - see Pig's Bay.