With the Trump National Golf Club clubhouse in the background, Camp Calleva kayak instructor Steve McKone helps one of his campers while teaching a lesson on the Potomac River on Monday. (Toni L. Sandys/The Washington Post)

The Trump family has offended many sectors of establishment Washington since their arrival in the nation’s capital, from Langley’s spymasters to mansion-dwellers in the District’s Kalorama neighborhood.

But 30 miles north of the White House, a conflict is now brewing on the banks of the Potomac River that pits the president’s interests against those of a very different — if no less zealous — constituency. This one is armed with paddles.

Citing security concerns, the Coast Guard says it is adopting a policy of periodically cutting off access to roughly two miles of the Potomac where it borders Trump National Golf Club in Sterling, Va.

The restrictions would clear the water of canoes, kayaks, stand-up paddleboards, sailboats, Jet Skis, motorboats and anglers when Trump or other senior officials of his government decide to spend a day on the back nine.

The buffer zone is stoking concern and opposition among recreational users of the river. The proposed shore-to-shore security area includes Riley’s Lock, the embarkation point in Maryland for a popular summer camp and a kayaking program for wounded and disabled veterans.

“It’s just heartbreaking,” said John Deitle, 41, a former Marine who served a combined five tours in Afghanistan and Iraq and receives treatment at the Walter Reed National Military Medical Center for lung problems he says are related to chemical exposure.

Deitle paddles on this stretch of the Potomac with Team River Runner, a nonprofit that helps wounded veterans. On Sunday afternoon, he stood in a life vest at his put-in point on Seneca Creek, a faded tattoo saying “Teufel Hunden” — “Devil Dog,” a Marine nickname — showing on one of his bare upper arms.

“Granted, it’s his golf course,” Deitle said. “But he has other golf courses.”

Battles over the presidential prerogative to make life inconvenient are a perennial drama in and around Washington. Former President Bill Clinton caused an uproar among crosstown commuters when, bowing to the wishes of the Secret Service, he closed Pennsylvania Avenue in front of the White House to auto traffic in 1995.

But such complaints have taken on a special resonance in the Trump era, perhaps because Maryland, Northern Virginia and the District voted overwhelmingly against the president, who brands himself as a brash interloper among Washington's swells. In March, the Secret Service's liberal blocking of precious parking space near the home of Ivanka Trump and Jared Kushner stirred a revolt among their neighbors in Kalorama. In April, the Secret Service barred pedestrians from the sidewalk along the White House's southern fence.

The sweeping new security measures proposed near Trump National seem to have come as a particular blow to the tightly knit clan of paddlers on this half-mile-wide section of the Potomac, which courses slowly past shores shaded by sycamore and black walnut before turning into light rapids.

“It’s a sharing culture out here, and it feels strange to have somebody not sharing,” said Ashley Nee, a kayaker who competed for Team USA at the 2016 Olympic Games in Rio de Janeiro and is training for 2020 on the affected stretch of river.

The U.S. Coast Guard announced it will periodically cut off access to roughly two miles of the Potomac River where it borders Trump National Golf Club in Va. (Video: WUSA)

It is not the first time Trump National has been the scene of a river-related controversy. In 2010, the golf club cut down hundreds of trees along the shoreline — an action that, some paddlers say, created the open sightline to the course that now compromises the president's security.

Officials at the White House and Secret Service did not respond to requests for comment.

Lt. Amanda Faulkner, a spokeswoman for the Coast Guard, said water-access restrictions would be invoked only when the Secret Service requested them because of visits to the golf course from “high-ranking government officials.”

She declined to say who qualified as “high-ranking,” saying the Coast Guard would take direction from the Secret Service on which officials triggered the security zone. Most of the time, she said, the river would remain open.

Faulkner said the Coast Guard had already closed the river next to Trump National five times since March on an ad hoc basis. One benefit of designating a “permanent security zone,” she said, was that boaters would now know exactly what was off-limits.

“In a lot of ways this is better for the public, because they have more information,” she said. Boaters would be notified of the closures by radio and online and perhaps through news releases, she said.

The policy is in effect on an interim basis, she said, and will be made final — and adjusted, if necessary — after the Coast Guard receives public comments that must be submitted by Aug. 9.

Authorities’ explanations for the rule have gotten a relatively cold reception among paddling organizations, which — not unlike other amateur athletic groups in the District and its affluent suburbs — have an inordinate share of bureaucratic know-how and ­legal firepower at their disposal.

On Sunday evening, representatives of various river groups convened an informal war council at the home of Canoe Cruisers Association board member Barbara Brown, who lives near the river in Potomac, Md.

Attended by 13 emissaries from different parts of the paddling community, the gathering was reminiscent of the Council of Elrond in "The Fellowship of the Ring," as the group debated its recourse against a seemingly implacable foe.

The Canoe Cruisers Association’s chairwoman, Susan ­Sherrod, a retired information-technology worker who was wearing a tie-dye shirt, presided over the gathering, which took place over Stella Artois and fresh cherries.

“This is a river-access issue. It’s not a political issue,” Sherrod said. Asked earlier by a reporter whether she had voted for Trump, Sherrod laughed uproariously.

Yet the political tension infusing the situation was unavoidable. One meeting attendee, Howard Morland, speculated that the regulation’s true purpose was to stop waterborne protests that groups from outside the region had begun staging during events at the golf course. Others wondered aloud whether impeachment proceedings would solve their problem before the end of Trump’s first term. The president’s avid golfing schedule during his early months in office put no one’s mind at ease.

“What they’re actually saying is, ‘We want carte blanche to shut down the river between these coordinates,’ ” said Adam Van Grack, a Bethesda attorney who chairs the U.S. Olympic organization for kayakers and canoers and represents Calleva, a summer camp and outfitter that launches its watercraft at Riley’s Lock.

Sherrod suggested they unite behind an alternative proposal that would modify the security zone to allow for a corridor of river access along the Maryland shore opposite the golf course.

Brett Mayer of the American Canoe Association, who called in to the meeting from the Thousand Islands in the St. Lawrence River, later said in an interview that he thought some form of compromise along those lines could be struck.

“It’s reasonable that the Secret Service and the Coast Guard are working together to create a secure zone. If there’s a motorcade in D.C., you might have to sit there for 20 minutes and wait for the motorcade to pass,” Mayer said. “These closures, they’re temporary, and they’re sporadic.”

He added, “We’ll do the best we can with the situation, but I don’t think it’s the end of the world.”