The Outer Trial Bank

This doughnut, known as the ‘Outer Trial Bank’, is one of two islands constructed during the 1970s to study the feasibility of converting the entire estuary into a fresh water reservoir.

The idea was to build a tidal barrage across half of the Wash to capture freshwater from rivers flowing into the estuary. The plan failed spectacularly because the banks were built using mud dredged from the salt marsh, which was saline anyway, and it salinated the stored fresh water. The plan was shelved but not after £3 million were spent in futile. Now these artificial islands have gained new importance as a breeding bird colony, with around three thousand pairs of sea birds using it as their nest.

Source Amusingplanet