Nore

The Nore is a sandbank at the mouth of the Thames Estuary, England. It marks the point where the River Thames meets the North Sea, roughly halfway between Havengore Creek in Essex and Warden Point in Kent.
Until 1964 it marked the seaward limit of the Port of London Authority. As the sandbank was a major hazard for shipping coming in and out of London, in 1732 it received the world's first lightship. This became a major landmark, and was used as an assembly point for shipping. Today it is marked by Sea Reach No. 1 Buoy.