Jeff Kagan, co-founder of the 6-year-old event in Boulder, said a record 19 people -- some wearing business suits over their wet suits -- climbed into inner tubes and floated on Boulder Creek at Eben G. Fine Park at 8:15 a.m. Tuesday, the Boulder Daily Camera reported Wednesday.
Kagan said the previous record was eight people, set last year.
"I'm surprised it took this long to grow," he said.
The city of Boulder set up a breakfast station for the event, similar to the 45 breakfast stations set up Wednesday morning for Bike to Work Day, which was being observed in Boulder and Denver.
"Our biggest thing is getting people to use any alternative mode of transportation," said breakfast station worker Niall Stewart of Boulder Public Works. "We're just happy to see people not sitting in their cars in traffic."