The princes, who have both served in the armed forces, joined a work crew In Datchet, west of London, from about 6 a.m. on what aides said was a private visit.
The princes were not the only royals helping out. Their grandmother, Queen Elizabeth II, has sent feed and bedding from the royal farms at Windsor to farmers whose land has been inundated.
England, which has been lashed by wind and rain since December, had its wettest January since records began in 1766, and the rain has continued this month. Storms this week have brought wind gusts of more than 100 mph (160 kph).
Floods have drenched the southwestern coast of England, the low-lying Somerset Levels and the Thames Valley west of London, where hundreds of properties have been swamped after the river burst its banks.
Another bout of gale-force winds hit the country Friday, bringing large waves and up to 1.6 inches (4 centimeters) of rain.
As winds gusted at up to 80 mph (130 kph), landslips and fallen trees caused havoc on the rail network, and some arriving flights were diverted from London's Heathrow to other airports amid fierce bouts of wind.
Peter Willison of the Environment Agency said Friday's rainfall would send waters on the Thames and other rivers even higher, flooding hundreds more properties.
He said it would be "many days," and possibly weeks, before flooded rivers receded.