BOULDER, Colo. -- Boulder police cited no one and received no complaints over the annual World Naked Bike Ride, which promotes bicycling over driving.

Police cracked down on participants this year, warning them that they could be cited and, if convicted, labeled sex offenders if they violated state law, which prohibits exposing genitalia in public.

“We support the rights of community members to protest in Boulder, but we are also responsible for enforcing the law,” said Boulder Police Chief Mark Beckner in a statement.

In the statement, Beckner advised protesters to wear “undergarments that cover genitalia or otherwise obscuring those body parts from public view.”

Some protesters wore briefs or thongs, while others donned more creative cover-ups, including fig leaves and small baskets. Some women rode topless or wore strategically-placed stickers or pasties, which does not violate state law.

Police were present at the start of the race and officers on bicycles and in patrol cars supervised the protesters as they cruised downtown Boulder.

Members of the ACLU, who were on-hand to observe the event, said the crackdown violated protesters’ first amendment rights.

“The ACLU supports the rights of individuals to engage in expressive speech and political speech,” said Judd Golden, Chair of the Boulder County ACLU of Colorado. “Law enforcement should be reserved for situations where there are victims, where people are being harmed. Simple public nudity is not one of those situations.”

“People are doing way cruder and ruder things than taking off their clothes, to our planet,” said Stele Ely, a protester who bicycled wearing only briefs, a straw hat and body paint.

The ACLU of Colorado is urging lawmakers to take up legislation that would exempt nude protesters from being labeled sex offenders if convicted of indecent exposure. Golden said he hopes the issue is addressed in the next legislative session.

A few dozen bystanders gathered at Pearl Street Mall to watch the semi-nude protesters whiz by. None said they objected to the nudity.

“I think it's very fitting for the town of Boulder and I'm really excited to see them,” said Nicki Ellingson, who was hoping to catch a glimpse of the riders.

“I came from Alabama to see some naked people!” said Rachel Parris, who was in town visiting a friend. “If they care that much about their cause, go for it.”

Parris’ friend, Carolyne Larson, a former pre-school director, said she did not think the protest was offensive or inappropriate, even for children.

“I think they did it very tastefully,” she said.

Stephen and Beth Cox, who were visiting with their young daughters from Corpus Christi, Texas said subjecting the protesters to laws that could result in sex-offender status was going overboard.

“We saw them last year and we saw them this year and we think it's kind of funny,” said Stephen.