More than 60 spectators at the Boat Race had to be rescued by lifeboat crews after getting trapped on the edge of the River Thames.
Video footage showed a group of at least 40 people stranded by the rising waters after watching yesterday's rowing race between Oxford and Cambridge universities.
A boy, reportedly eight years old, was also rescued from an embankment after he became separated from his mother, while seven people were evacuated from Chiswick Eyot when they were cut off by the rising tide.
The RNLI said it was a "surprise" to find so many spectators in trouble and the number was "significantly greater" than in previous years.
Many were unaware that they would be exposed to the substantial wash from the flotilla following the races and from the rising tide, it said.
As a result many were cut off and found themselves with limited options to reach higher ground, the RNLI added.
Chiswick RNLI station mnager Wayne Bellamy said: "This incident showed once more that the tidal Thames can catch people unaware.
"Whilst RNLI Lifeboats have rescued a number of spectators of earlier boat races, the numbers in trouble on Saturday were significantly greater than previous years.
"Thankfully the diligence of our three RNLI Lifeboat crews and the contribution of the Royal Marines and police boats ensured that nobody came to serious harm."
Thousands of people watched from the sidelines as Oxford's male and female crews powered to victory in their races
It was the first time the women's team had rowed the same course as the men and on the same day in the 87 years they have competed.