Londons Thames Barrier, 2 miles down stream from the Isle Of Dogs, became operational in 1984 and was constructed to protect central London, which is essentially a floodplain of the Thames, from exceptional high tides and storm surges from the North Sea. The seeds of the barrier were sown following the North Sea flood of 1953 when a lethal combination of a spring tide, severe winds and low air pressure caused sea levels to rise by up to 5.6 metres above normal levels resulting in the deaths of 307 people in England.

The barrier is essentially a set of rotating gates, the concept being devised by Charles Draper in 1969 and was based simply on the design of the gas taps on his parents cooker! The gates themselves are hollow circular steel segments, each weighing 3,700 tonnes and reaching just over 20 metres in height. The entire structure is across a section of river 520 metres wide between Silvertown to the north and Charlton to the south. This section of the river was chosen due to the strong chalk riverbed and the straightness of the banks here. In addition to the barrier, the defences along the riverbank were raised and strengthened for 11 miles downstream; there would be no point holding back the water only to see it spill around the edges!

Construction began in 1974 and the barrier was officially opened by the Queen in 1984. The total cost of the project was over £500m (£1.6bn in todays prices) with a further £100m (£320m) spent on the 11 miles of upgraded river defences.

The barrier is set between nine piers (and two riverbanks, of course) giving ten individual barriers and, when open, the gates lay on the river bed allowing shipping to pass through six of the gates normally. The two gates nearest to each riverbank are not navigable. When forecasts indicate that central London will be subject to water levels in excess of 4.87 metres the gates rotate and form a barrier against the tide.

As of February 2018, the barrier has been closed 182 times, with 50 of these closures being seen between September 2013 and April 2014.