The Marchioness disaster occurred on the River Thames on August 20, 1989, when the pleasure boat Marchioness sank after being run down by the dredger Bowbelle. The two boats collided under Cannon Street station bridge. 51 of the 132 passengers on the Marchioness attending a private birthday party were drowned. Many of the victims were young people working in the fashion industry, and included Francesco Dallaglio, sister of future England Rugby captain Lawrence Dallaglio.

The disaster was found by the Marine Accidents Investigation Board to have been caused by the poor visibility from each ship's wheelhouse, the fact that both vessels were using the centre of the river, and that no clear instructions were given to the look-out at the bow of the Bowbelle. The skipper of the Bowbelle, Douglas Henderson, was tried for failing to keep a proper look-out but after two juries were deadlocked he was formally acquitted.

A Coroner's inquest on April 7, 1995 found the victims had been unlawfully killed. John Prescott as Secretary of State for Environment, Transport and the Regions ordered a judicial inquiry under Lord Justice Clarke on August 18, 1999.

See also

• List of United Kingdom disasters by death toll
• List of wars and disasters by death toll (worldwide)
• List of disasters (by subject)