Their mission: To make contact with boaters crossing the international border in the middle of this 11-mile long lake that sits half in Canada, and half in the United States.
The contacts help keep boaters informed of what's allowed and what's not when they cross the invisible line bisecting this mile-wide lake.
The patrols are just one way that the U.S. Border Patrol keeps an eye on water crossings.
Remote cameras, tips from the public and sightings from the air also alert the agents in charge of protecting the border. But regular boat patrols let boaters know in a very public way that they're out there, watching.
"This year, we're putting more emphasis on the water," says Kolo Moser, agent in charge of the U.S. Customs and Border Protection station in Oroville. "It's part of the border, and we're charge of protecting it."
This summer, agents are trying to stop and contact most of the boats that cross the border to inform them about two programs that allow them to land on the other side, if they have filed the paperwork, and have documents with them. They're called NEXUS and I-68 forms.
Without it, boaters are allowed to cross the border, but they're not allowed to land or contact anyone without physically reporting to the Customs and Border Protection office.
As some boaters are finding out, getting stopped on an international lake isn't like an ordinary traffic stop.
Law enforcement agents are allowed to search any vessel on this lake, without a reason or cause, Moser says.
Whether a boater has crossed the border or not, their boat is subject to being searched, he explains.
"It's a customs regulation that allows us to do that. It's very long-standing," he says, and did not come with new authorities following Sept. 11.
The authority didn't seem to bother any of the boaters enjoying Lake Osoyoos on Aug. 6.
It's almost noon and 87 degrees in the cabin of this 21-foot Sea Arc when Brent Olynyk zooms across the border on his vessel from the Canadian side.
Joe Flores, U.S. Border Patrol vessel commander, spots him and is ready to turn around when Vince Clark, also a vessel commander, advises, "Just slow down. Let him come to us."
When the vessel passes, Flores puts on his blue lights and the boat stops.
At once, they recognize him as someone they stopped just the day before.
"In the seven years I've been coming here, this is the second time now twice in two days," he tells them.
But still, they go through the routine.
"Do you have any ID?" asks Agent Jon Speiker, dressed in a blue Border Patrol uniform with long pants and boots, sunglasses, gunbelt and other gear.
Wearing only a swim suit, Olynyk hands him a plastic bag with is identification, and Speiker takes down the information and calls it in to his office.
"Do you have any cash over $10,000 or any weapons on board?" he asks.
"No," the Alberta resident says, adding, "You're welcome to come aboard."
And they do, looking in the seat compartments and in all the empty spaces on the vessel.
With the questions asked and answered, the conversation lightens when Clark admires Olynyk's vessel, and then asks him what he's doing on the lake today.
Olynyk says he's looking for property, maybe a little house on the lake in the U.S. "It's gotta be on the water," he adds.
Clark offers the name of a real estate company, and tells him about a small white house a ways downlake.
Despite the inconvenience of being stopped by the Border Patrol for a second day in a row, Olynyk says he's not upset by it. "You've got to expect it on a lake that crosses the border," he says, adding, "It would be more concerning if they're not checking."
Most of the boaters stopped on this afternoon have similar reactions.
One woman and her son on a personal watercraft are surprised to learn they had already crossed the border, and apparently believe they're in trouble.
But Clark reassures them that they're allowed to cross the border on the lake. They just can't make land, or make contact with another boat or person on the lake after crossing.
Others express comfort in knowing the Border Patrol is here. Some boaters even seek them out.
Robert Hingston, of Vancouver, B.C., zips toward them on his personal watercraft, and pulls up alongside their vessel to ask them about the requirements. He has a place on the U.S. side, and wants to make sure his daughters have everything they needed before sending them out on the water by themselves.
Clark says most of the people they stop are from Canada. That's because this lake is one of British Columbia's most popular destinations.
Known for its warm waters and sunny days, Lake Osoyoos attracts people from across Western Canada.
"We love coming down here," says Shauna Kozak, who is also stopped on the lake enjoying a day out with her husband, their two teenagers and three of their kids' friends. "We live just outside Edmonton, where it's cold eight months of the year. Down here, it's always sunny. It's always warm," she says.
By now, it's late afternoon, and 96 degrees in the Border Patrol vessel's cabin. Two small fans are working full-time, but with little effect. The lake is warm by Pacific Northwest standards, but still much cooler than the air temperature.
Glenn Stewart, of South Surrey, B.C., says he heard the lake temperature is 78 degrees today. He's been coming to here with his family for seven or eight years. His daughter and their two friends were just about to jump in to cool off when they're stopped by Customs and Border Protection.
"I actually think it's a really good idea," he says of the stops. "The reasons they have for pulling people over are all very valid. Arms smuggling, drug smuggling, boat theft. They're making sure everybody's safe on the water. We're totally in support of them doing this," he says.
Even on this hot August day, the U.S. Border Patrol agents onboard agree that patrolling Lake Osoyoos is a coveted assignment. But anyone tagging along can see this is no picnic.
To get here, the vessel commanders take a 30-day intensive course. It teaches them about the equipment inside a Border Protection vessel: Radar, GPS, a night vision scope, lights, fans, a siren and a spotlight, along with water pressure meter, engine temperature gauge, and other gauges to make sure the boat is operating properly.
When they're finished with the book work, there's the physical test. Clark says to pass, an agent has to swim a mile in full uniform including boots then tie a bowline knot in a rope hanging from a boat in the water, put their foot in and climb aboard.
"If you don't pass, they send you home. There's no breaks," he says.
That's because, although on this day there are no arrests, they must be prepared to chase and apprehend someone who wants to get away.
It doesn't happen often, but it does happen.
In one of their largest cases, Moser recalls apprehending two Canadian men who crossed the border on Lake Osoyoos in an 18-foot canoe, loaded with 478-pounds of marijuana. It was in April 2003, and the men used an electric motor, and hovered close to the shore.
But a Border Patrol agent with night vision equipment spotted them and they were caught and arrested for importing marijuana and possession with intent to deliver.
Although their boat patrols are mostly in the daytime, during the summer, they're watching Lake Osoyoos all the time, he says.
"Being the bad guy, they can come across any time," Moser explains. And while some try to slip through in the dead of night, others may attempt to blend with the recreation crowd.
This summer, Border Protection agents have made a lot of contact with boaters. They stopped and talked to 96 vessel owners in just one week. So far, there have been no major incidents, or arrests, but boaters out on the water on this day know they're being watched.
While patrolling the lake is a serious task, these agents are also personable with the boaters they stop.
"It's a fun job. You get to ride in a boat," says Clark, "but it does get warm."