Royal Marines will patrol the banks of the Thames this afternoon to ensure there is no repeat of last year's incident in which a swimming protester halted the Oxford-Cambridge boat race.
Using thermal-imaging equipment, marines in 10 inflatable craft will be scanning the river for any sign of disruptions, reports the Daily Mail.
Last year Australian Trenton Oldfield swam out into the river and was almost hit by an oar from the Oxford team, forcing the race to pause.
When the race re-started there was a clash of oars, and Cambridge took the lead to claim victory.
Executive director of the Boat Race David Searle said: "We are taking additional measures this year and have reviewed all of our actions last year in detail.
"There will be an increased presence both on and off the water, including support from the Royal Marines, but as with any security plan I cannot disclose the exact details.
"What I would say to anybody thinking of disrupting the race is that it's unbelievably dangerous. You risk injuring yourself, the crews and the other people following the race. Nobody wants that. This is just a sporting event."
Oldfield, 37, who served seven weeks of a six-month jail sentence for causing public nuisance, told the Spectator that he was not planning a re-run of last year's protest at government cuts, and will spend the day walking in the Cotswolds.
Police contacted Oldfield by post and by Twitter to ask him if he planned to attend the race to help him exercise his "lawful rights [to protest] without causing disruption or danger to themselves or others".
Oxford go into the 159th race this afternoon as strong favourites.
Team spokesman Joe Crilly said: "Oxford are certainly the best backed crew as of yet, although that was very much the case at this stage last year.
"Last year, however, we took nearly £40,000 on the day of the race and Cambridge became best backed by the time the race started. Maybe history will repeat itself this time around."