Coordinates: 51°29′52″N 0°02′12″E / 51.497744°N 0.036679°E / 51.497744; 0.036679

River Thames Flood Barrier

The gate in the middle of this view has been raised to the maintenance position; a barge can be seen in the foreground.

The Thames Barrier is the world's second-largest movable flood barrier, after the Oosterscheldekering in the Netherlands. It is downstream of central London. Its purpose is to prevent London from being flooded by exceptionally high tides and storm surges moving up from the North Sea. It is raised (closed) only during high tide; at ebb tide it is lowered to release the water which backs up behind it.