A paddleboarder wearing only a swim suit, gliding down Shem Creek -- the image is so laid back it says summertime.

There's just one thing: It's not legal.

For three years now, paddleboarders have been required by federal law to have a personal flotation device, or PFD, the sort of life preserver that kayakers wear, and carry a distress whistle. Surprised? So are a lot of the casual paddleboarders who have been stopped by state wildlife officers or U.S. Coast Guard patrols this year.

The two agencies this summer stepped up enforcement with the sudden boom in the stand-up water sport's popularity here. What was a handful of paddlers a few years back became hundreds this summer.

"There is more enforcement going on than there ever has been," said Dave Clifford of Charleston Watersport Outfitters in Mount Pleasant; the shop rents and sells the boards. Its staff recently was warned by a S.C. Department of Natural Resources officer after a paddler on one of its rental boards was stopped on Shem Creek without a PFD.

"They definitely have stepped it up. All the people I paddle with are pretty seasoned, and we either have been ticketed or pulled aside and warned," said Dean Johnson, perhaps Charleston's highest-profile paddler. Johnson is a professional racer, a paddle board maker and a competitor in the annual Shem Creek Shootout paddleboard race this weekend.

Johnson recently bought himself an inflatable waistband PFD after drawing a third warning on the water since the law was put on the books in 2008.

He doesn't like it much. It's funny, he said, how you're not allowed to paddle a board around without one but can ride a motorcycle without a helmet.

"I just use it because I don't want to get hit with a ticket," he said.

A ticket isn't a slap on the wrist. The fine ranges from $200 to $475, depending on circumstances, said DNR Lt. Robert McCullough. "It's always officers' discretion (whether to write a warning ticket or citation) out there."

PFDs are not required if the boarder is surfing. The Coast Guard classified a paddleboard as a vessel in 2008 after concerns rose in Oregon over the number of boarders in the heavily boat trafficked Columbia River. The sport, which began as a surfing sport, had morphed into a flat water pastime similar to kayaking. The move put the craft into the same category as kayaks or canoes, which require the safety devices.

"There's not a lot of difference in flat water than sitting in a canoe and paddling," McCullough said. The department increased its focus on violators after the Coast Guard issued a notice, he said. McCullough could not say how often paddleboarders have been warned or fined; the citation written is the same as for a life preserver violation on any sea craft.

Coast Guard officers did not call back The Post and Courier on Tuesday after being asked for comment.

"I think overall a PFD is a good idea," Johnson said. But he doesn't think it should be law. "For experienced swimmers it's not so important."

But it is what it is, Clifford said.

"Every other boat out there uses PFDs" from kayaks to outrigger canoes to canoes, he said. "If that's the rule and they're going to enforce it, we've got to follow it."

Reach Bo Petersen at 937-5744 or Twitter at @bopete.