The pleasure boat The Marchioness collided with another vessel and sank with the loss of 51 lives. In nearby Southwark Cathedral there is a Marchioness memorial stone.
The following comes from a BBC report of the 20th anniversary of the Marchioness disaster: "The Marchioness had been hired to celebrate the 26th birthday of Cambridge graduate Antonio de Vasconcellos. On board were high-flyers from the worlds of finance and fashion, including Francesca Dallaglio, sister of former England rugby captain Lawrence Dallaglio. More than 130 partygoers were on the Marchioness when it collided with a dredger, the Bowbelle. A Marine Accident Investigation report blamed poor look-outs on both vessels." Chron used to give some details and many of the names of the dead but, 2014, that's now a dead link. We can't find the full list anywhere.
Our colleague, Alan Patient, points out the location of the three plaques contradicts the reports of where the accident happened. Wikipedia says "near Cannon Street Railway Bridge" - that's five bridges further downstream from the most downstream of the three plaques.
2014: Londonist reports the Southwark Cathedral memorial service planned for the 25th anniversary.
