Hundreds of spectators braved the marshy mud and mosquitoes in Virginia Wednesday to watch the 90th annual Chincoteague pony swim – even if it meant losing a shoe.

The pony swim from Assateague Island to Chincoteague Island on the eastern shore was led by a group of volunteers called the "Saltwater Cowboys," who round up the ponies and lead them through the passage at slack tide.

The tradition was made famous by Marguerite Henry's 1947 fictional book "Misty of Chincoteague,” which is based on the event.

An auction of a portion of the herd on Thursday will benefit the Chincoteague Volunteer Fire Department. The auction helps the department comply with a directive from the National Park Service, which allows only 150 horses to stay on the island, Delmarvanow.com reports.

Diane Huntley of Fredericksburg, Va., told the Baltimore Sun that she put her foot in the mud to get a glimpse of the swim and when she lifted her leg, her shoe was gone.

"I didn't want to stick my hand in to get it," she said. "I think bare feet would probably have been best."

The event poses a challenge for spectators, according to the newspaper. Some people crane their necks to see the ponies from a waterside park, while others enter the mud to get a closer view.

"We just had to stop and watch it," Sharon Hammond of Woodbridge, Va., told the Baltimore Sun.  "It was amazing. I couldn't even take pictures because I was mesmerized."

The swim began at 8:15 a.m. and ended around nine minutes later. After a 45 minute rest, the Saltwater Cowboys started to herd the ponies to the carnival grounds where the auction will take place.

Several ponies escaped from the herd en route to the carnival grounds, frolicking through front yards and weaving through spectators, Delmarvanow.com reported.

After the auction, the herd – minus a key player this year, Surfer Dude – will swim back to their Assateague Island home on Friday.

During his 23 years, Surfer Dude often led the swim to Chincoteague. He was found dead this spring, leaving dozens of ponies he sired to continue his legacy.

The Associated Press contributed to this report.