Flodstrom, 40, was arrested Tuesday at the Oak Street Beach in Chicago.
He was handcuffed by police while still in his cold-weather wetsuit and taken to jail, where he was detained for 4 hours on a disorderly conduct charge, the Chicago Sun-Times reported. His trial is set for Feb. 16.
A Chicago surfing ban ended in 2009 after authorities were pressured by advocate groups, but surfing remains heavily regulated on the city's beaches. The sport is limited to certain beaches, Oak Street not being one of them.
Slater said he is baffled by Chicago's tough surfing regulations.
"It makes no sense … it sounds like a police state," he told the Sun-Times.
Advocate groups plan to show up to court along with Slater to re-energize a push for expanded surfing in Chicago, members said.