The doughnut in the wash..
Actually I just found this...
"1972: a feasibility study commissioned by the Government to build a barrage across half of The Wash to capture the freshwater from the four main rivers, to improve navigation through sea locks, to provide recreational facilities and an area of land for a power station, etc. was undertaken. This led to the circular trial bank/bund being built to the east of Sutton Bridge and the Nene. The purpose of which was to act as reservoirs but the report concluded it would be too costly."
TC
P.S. sorry nuffin to do with aviation