The pleasure boat Marchioness sinks on the River Thames following a collision. Fifty-one people are killed.

The Marchioness disaster was a collision between two vessels on the River Thames in London in the early hours of 20 August 1989, which resulted in the deaths of 51 people. The pleasure boat Marchioness sank after being hit twice by the dredger Bowbelle at about 1:46 am, between Cannon Street railway bridge and Southwark Bridge.

The River Thames, known alternatively in parts as the River Isis, is a river that flows through southern England including London. At 215 miles (346 km), it is the longest river entirely in England and the second-longest in the United Kingdom, after the River Severn.