AUSTIN (KXAN) — Swimmers and boaters beware.

Travis County Parks are warning about the hazards that zebra mussels pose to swimmers and boaters ahead of the holiday weekend.

“The public is urged to wear water shoes, tennis shoes, or any sturdy closed-toe footwear; socks offer limited-to-no protection,” officials wrote in a press release Tuesday. “People are being advised to be careful where you place your hands and feet upon entering or exiting the water and when near underwater rocks or structures.”

The mussels’ shells are sharp and can easily cut bare skin and most lightweight clothing, officials said. Since the start of this year’s swimming season, Travis County Parks officials have recorded dozens of people with injuries caused by mussels.

CLEAN UP! Texas boaters encouraged to thoroughly clean equipment to stop spread of zebra mussels

Travis County parks on Lake Travis where officials say there’s been an “explosion of the growth of zebra mussels” include:

Arkansas Bend

Bob Wentz

Cypress Creek

Hippie Hollow

Mansfield Dam

Pace Bend

Sandy Creek

Tom Hughes

Toni Sponsler swims at Sandy Creek park at least once a week. She told KXAN Tuesday that the shells of the zebra mussels regularly leave her with cuts because they’re mostly shielded from view and are heavily clustered underneath rocks along the shore.

“They’re like razor blades,” Sponsler said. “It feels like glass, but it’s never glass. It’s always the mollusks.”

She said she always warns her friends and other visitors that they’re most likely to get hurt getting in or out of the water.

“They are literally up against the rocks over here on the shore,” Sponsler said, pointing to a handful of zebra mussels she fished from the water. “It’s the worst part when the waves come in, and you’re trying to get out and you slip and then you’re cut.”

Most hard surfaces below the waterline are covered in zebra mussels in these water bodies, officials say. At least 15 Texas lakes, including Lake Travis, Lake Austin and Lady Bird Lake, along with five river basins, have been fully-infested with the mussels so far, officials say.

Aralyn Vragel, a 15-year-old kayaker, said she once went on a party boat on Lake Travis and couldn’t climb back into it because the crew warned about the zebra mussels on the sides cutting her.

“I sometimes don’t want to get in the water with my bare feet because I’m afraid of them being there,” Vragel said. “No one wants to get their foot cut in the water.”

Zebra mussels are an invasive, finger-nail sized mollusk that are native to the fresh waters of Eurasia. Officials say they arrived in North America on boats in the 1980s, invading the Great Lakes region and spreading over the rest of the continent.

The mussels wreaked havoc in Austin when dead mollusks in the city’s water supply caused thousands of Austinites to experience a foul, sewage-like smell emanating from the water coming from their faucets.

The Texas Parks and Wildlife Department is constantly monitoring lakes in the state to watch for the spread of the species. They’ve created a new website to help marinas and boat owners learn how to properly decontaminate their equipment and inspect them before moving to a new spot.

If you see zebra mussels in a lake where you haven’t before, you’re encouraged to call the Texas Parks and Wildlife Department at (512) 389-4848.