One day a year for the past four decades, dozens of Islanders have converged on the same swampy piece of ground west of town to drive jacked-up trucks and Jeeps through several feet of mucky water.

They also gather at the same time each year — the Friday that marks the start of the Strawberry Festival.

This year, however, was likely their last. The site is now owned by King County, and last Friday — after some drivers moved huge concrete blocks to gain access and ended up with most of their trucks marooned in the deep, brown water — sheriff’s deputies arrived and told them they had to leave.

Police have shown up in years past, said Islander Roger Sherman, who’s been “mud-bogging,” as it’s called, since he was 5. “But this is the first time they’ve ever shut us down,” he said.

Sherman, who went this year to show his 11-year-old daughter what the annual event is like, said he’s frustrated that he and his fellow mud-boggers can’t use county land.

“This is county property. Shouldn’t we have the right to use the park?” he asked.

“The horseback riders have everything,” he added. “It’s wrong. It’s just completely wrong.”

But Joe VanHollebeke, a resource coordinator with the county’s Department of Natural Resources and Parks, said mud-bogging is too ecologically destructive to take place on county-owned lands.

Last week, he walked through the area, a 40-acre swath purchased by the county in December and contiguous with the popular Island Center Forest. Deep, muddy ruts — some of them extending along an old road for several feet — led to the site, making walking difficult. Standing pools of water were brown. At the actual site of the bogging, deep tire tracks carved a wide path into a large, mucky pond.

“The whole point of what they do is counter to the whole point of what we do,” said VanHollebeke.

The wetlands form the headwaters to Judd Creek, Vashon’s largest watershed and a salmon-bearing stream. The county’s goal, VanHollebeke said, is to provide open space for passive recreation and to protect what he and others believe are important ecological resources.

Indeed, a county crew only last week began working on a new trail that will lead walkers, horseback riders and runners through the new property, connecting them with the nine miles of trails that currently exist in Island Center Forest. Damage from this latest round of mud-bogging, VanHollebeke said, will likely double both the time and costs it takes to construct the new trail.

“I’m disappointed and frustrated that right when we’re making some progress, the place gets torn up,” he said.

The wetland has been a well-known mud-bogging site for around 40 years, Sherman said. His father, John Sherman, helped to start the tradition, building a small dam and turning what was “a little mud hole” into a full-fledged pond.

Over the years, the one-day event grew in size, sometimes drawing as many as 600 people, many from other parts of the state, Sherman said. Families with children would come, picnicking in the backs of their trucks. Some mud-wrestled, he recalled. Music from car radios filled the air.

A home-made video of the event from 1999 shows a few jacked-up trucks making their way slowly through the pond, spraying water and mud when the going got difficult, while groups of people stood a safe distance watching, laughing and egging on the drivers.

“It was a lot of fun,” Sherman recalled.

In recent years, fewer people have shown up, in part because the bogging has grown more difficult as the pond has gotten deeper from all the activity. Indeed, this year, Sherman said, all of the trucks that attempted to cross the pond got stuck. His “swamp buggy,” as he dubs the rig he uses, was called into service, working as a tow truck Friday and Saturday.

Sherman said he realizes the trucks gouge out the road and create enormous ruts, and he plans to help the county repair some of the damage. At the same time, he’s frustrated that there is no public place for what he considers a traditional Vashon activity.

“We don’t want to have problems with other people. We just want to go out once a year and have our little mud show,” he said.

He hopes to work with the county to find another place where mud-bogging can happen. A former cow pasture with some water trucked in would work, he said. “I hope they’ll listen to us,” he said.

County officials said they encourage the mud-boggers to come to the monthly Friends of Island Center Forest meeting. Those who regularly attend the meeting say representatives from the mud-bogging community have never attended.

At the same time, county officials said, it’s unlikely they’d ever allow such activity on publicly owned lands and certainly not at Island Center Forest. “We’re hoping to reach out to these people and help them understand what our goals are,” said David Kimmett, a natural lands manager with the county.

“We’re not out to judge the activity,” he added. “But clearly, this is not what we have in mind for the site.”

Meanwhile, he said, the county is well on its way to connecting what he and others call the “gateway site” to the rest of Island Center Forest, creating a 400-acre swath of forestland that people will be able to reach from town. A crew began the process last week, flagging a trail that will eventually wend all the way to the main entrance of Island Center Forest at S.W. 188th Street.

The Vashon-Maury Island Trust and its AmeriCorps crew will donate a week to the trail-building effort, and a large volunteer work party is scheduled for Aug. 18, Kimmett said.

After months of work, he added, the new parcel is now free of debris from a homeless camp that had long existed there. It’s hardly pristine, he said, but nature is beginning to reclaim the site.

“It’s already starting to feel like it’s a natural place,” he said.