PORTLAND – The Coast Guard has been riding on and providing escorts for Casco Bay ferries.

The Coast Guard increased its presence on and around the ferries in response to the orange threat level issued for public transportation by the Department of Homeland Security.

The new procedures began before Thursday’s incidents in London, but were in response to the July 7 bombings of London’s public transit system, which killed 56 people.

But the idea of a Coast Guard boat with a gun mounted on its bow escorting a ferry is alarming to some islanders and pleasure boaters.

“The chances of an al-Qaida attack on a Casco Bay Lines boat are pretty remote,” said Howard Kessler, a part-time resident of Peaks Island who figures that the security patrols are mainly for show.

The Coast Guard said its escorts and personnel riding the ferries are designed to provide a sense of security, as well as achieving the real thing.

“The purpose of having an escort is to keep the ferry safe not only from the inside but from the outside,” said Coast Guard spokeswoman Kelly Newlin. “The threats are not only on board with a bomb, but could be a terrorist coming from the outside.”

The elevated security covers all ferries nationwide that can carry 150 passengers or more. The Coast Guard has been providing occasional escorts with its 25-foot rigid inflatable boat, as well as having officers riding the ferries with an eye out for suspicious people or packages.

Government officials said earlier this month that they have no specific intelligence indicating a direct threat to ferries, but that it was prudent to increase security on ferries, which carry more than 135 million people each year.

But some say new security measures run counter to the idea of island life.

“I perceive it as my civil liberties are yet again being infringed upon for the sake of some government paranoia,” said Martha Mickles, who watched from her cottage on Little Diamond Island as the Coast Guard escorted the car ferry Machigonne II last weekend.

“It’s scary for me, in my own pleasure boat, if I have to go to town at the time these guys are going or coming back,” she said. “I have to make sure I’m a certain distance from the boat.”

Philip Lee said a Coast Guard patrol boat narrowly missed his 20-foot pleasure boat last Saturday as he motored from the town wharf to a nearby private dock.

“In a flash, the rig with the machine gun and all the cowboys on it were right on my port bow,” he said. “I had the right of way, but that wasn’t the rules they were playing by.”

He was told later by the local Coast Guard office that the Coast Guard boat was involved in a drill.

Newlin said the Coast Guard officers assigned to ride the ferries are trained to identify and secure any kind of risk. She said there are no set schedules on which ferries they will ride.

“It is random,” Newlin said. “They want to make sure they’re checking everybody and everything. If they stayed on one certain ferry and only on that ferry, that’s not very effective.”