Boaters heading to the St. Croix River for the season’s first big holiday weekend will find an unprecedented roadblock of construction barges and a mile-long no-wake zone.

Water traffic near Oak Park Heights on a stretch of the popular waterway known for fast boats will be slowed to a crawl for the next four summers to protect workers and construction equipment that have started to move into place at the site of the new St. Croix bridge.

“I haven’t met anybody who’s against it,” said boater David Anderson of Eagan, who was buying supplies at the Bayport Marina gas dock on Friday. Problems with big wakes slamming boats at Sunnyside Marina, near the new no-wake zone, have resulted in injuries including broken limbs, said Anderson, a member of the St. Croix Yacht Club.

“The speed boaters like to go up and down the river as fast as they can. If somebody thinks of safety of people in the marina they’ll think like me. There will always be some people who don’t like no-wake zones.”

Signs of construction on the five sets of massive steel-reinforced concrete piers that will support the bridge can already be seen on the river as barges bearing huge cranes move into place.

Along with slowing down to no-wake speed, the minimum needed to keep watercraft moving, boats will be funneled from either end of the site to a 300-foot-wide channel between two of the piers to pass by. The hourglass-shaped navigation channel through the two piers will be marked by red and green buoys that were being put into place on Friday, said Mary McFarland Brooks, spokeswoman for the Minnesota Department of Transportation (MnDOT). No boat traffic will be allowed between the buoys and shorelines on either side.

The first step in the process of building the piers will be construction of coffer dams — temporary watertight enclosures — around which their foundations to the bedrock beneath the riverbed will be drilled and poured. The no-wake zone is needed to minimize wave action that would disrupt that construction or the flotillas of barges that are lashed together carrying the heavy construction cranes that could start wobbling and tipping.

On another Bayport Marina dock Friday, Todd Meissner of Lakeland was taking his family onto the river for an afternoon ride. “I see it as just another chokepoint,” said Meissner, who has boated on the St. Croix for years and said most boaters have become accustomed to no-wake zones in several areas up and down the river.

“There are a lot of people who support the [new] bridge and a lot of people opposed. I think it will be better for Stillwater. I think the bridge is going to be a big improvement,” he said.

The extra congestion and construction activity around the bridge site might drive some boaters to find other locales to enjoy the brief window of summer, “but I think the St. Croix is big enough to accommodate everybody,” said Susan Lutterman, executive officer of the St. Paul Sail & Power Squadron, a boater education and safety group. “We’ll still have plenty of room.”

The new no-wake zone just might be another good reminder of the dangers of excessive speeds in crowded waterways, she added.

News of the no-wake zone cheered Rick Chapman, general manager at Sunnyside Marina, where wakes from passing boats have caused problems for years. The marina is just north of the bridge construction.

“We are thrilled. We’re dancing in the streets here at Sunnyside,” Chapman said. “People are not particularly courteous to us.” Chapman said he lobbied “quite hard” for a no-wake zone skirting his marina in 2007 but said most people didn’t want one. “Most of the other marina operators and the boaters for that matter feel that you set up one wake zone in an area it’s only a matter of time before other people want wake zones,” he said.

Many boat owners in the marina’s 254 slips have reported wakes that range in intensity from tipping over a glass of wine to knocking televisions off their stands, he said. Fifty-foot houseboats at the gas dock were pitched 3 feet side to side when giant wakes hit the marina, he said.

Construction of the four-lane, $629 million bridge creates a necessary no-wake zone that everybody should accept, Chapman said.

“I think everyone understands that safety is paramount,” he added.

At Bayport Marina, about a mile south of the construction, general manager Cliff Lewis said the no-wake zone will inconvenience boaters but they’ll adjust. “They’re going to complain. They’ll get through it,” he said.

North of Stillwater, at Wolf Marine, co-owner Eric Wolf said he’s supportive of the no-wake zone as long as it’s temporary. “It’s a matter of safety for the people building the bridge. I think it’s a necessity,” Wolf said, adding most boaters tend to observe the other no-wake zones along the St. Croix, a National Scenic Riverway.

From the mouth of the Apple River to Taylors Falls is a designated “slow speed zone” on the St. Croix. And in six spots from the Arcola High Bridge to Prescott, Wis., there are no-wake zones as well. Boaters are also required to slow to no-wake speed within 100 feet of islands and shores, 100 feet of swimmers and when water levels are high.

Five agencies — sheriff’s offices in Washington and St. Croix counties, Natural Resources departments in both Minnesota and Wisconsin and the National Park Service — all have a part in enforcing the rules and making sure boaters are safe. Boating-related fatalities on the St. Croix are rare — a man who fell from a boat and drowned in 2012 was the first in a decade. A horrific nighttime boat collision in 1999 killed five people.

“We’re a regular presence out there, and I think that really helps,” said Cmdr. Jerry Cusick, who supervises the water patrol of the Washington County Sheriff’s Office. The county has two patrol boats, where crews emphasize educating boaters as much as enforcing the rules.

Cusick said he is not expecting major problems or costs with the added no-wake zone. But if it becomes apparent that more patrols are needed, including during off-peak times, that issue will have to be addressed, along with how to share the costs.