FOLLY BEACH - The sea lately has been a crystal blue people say they haven't seen here before.

"I almost fell over when I saw it. It's tropical," said Vern Beaver, of James Island. "It's usually a chocolate brown color."

The reason why is a bit of a mystery. People have speculated the renourishment dredging is causing it, but U.S. Army Corps of Engineers staffers say the work would be more likely to stir up the sands, clouding the water. They haven't come across anything like this in earlier projects.

"I really don't know why it's happening. But, boy, it was gorgeous when I was out there (last week). It was like I was in the Caribbean," said David Warren, Army Corps project manager in the Charleston district.

Whatever it is, it doesn't seem to be happening on Kiawah Island or Isle of Palms, according to Charleston County Park and Recreation Commission staffers.

But folks are ogling the sea from the commission's Folly Beach fishing pier and stopping by the pier office one after another to comment on it, said Alexis Mock, park attendant. Long-timers say it's a prettier blue than its ever been.

"Even the bartenders who are out here all the time are saying it's like working at Sandals," said Kristin Meyers, of West Ashley, referring to the posh tropical resorts.

The usual brownish, clouded color of the nearshore waters is from stirred-up sand and silt, said College of Charleston oceanographer Jack Ditullio.

"The blue color just comes from the blue (in the spectrum of) light scattered more effectively," he said. The sands and silt might have settled with the drier weather and slower flow of water out the estuaries, he said. And there just might be something to that. Along with dry weather, tides settled recently, dropping from a range of 5 to 6 feet between high and low to 3 to 4 feet.

If so, the blue might be about to roil away. Thunderstorms are forecast for Thursday and the tide range is forecast to start climbing again.

But the bluer than blue seas have put a new mellow into the settled-in Folly vibe. Meyers enjoyed it from the gazebo at the end of the fishing pier on a recent afternoon, surrounded by regulars chatting it up and laughing, she said.

"It's insane how crazy beautiful it is," she said. "Nobody has any answers. It's just a mystery, but we'll take it."

Reach Bo Petersen at 937-5744, @bopete on twitter or Bo Petersen Reporting on Facebook.