It’s the Coast Guard that is summoned for nautical emergencies, such as when a sailboat takes on water in the Chesapeake or a fishing boat is in trouble in the Atlantic off the Maryland coast.

But someone in the Washington region, the Coast Guard says, has been sending distress calls for the past two years for emergencies that did not exist. The service said the caller has made 28 “hoax calls” since July 2014.

The calls originate in Annapolis, the Coast Guard said Friday, and they are looking for whoever has been making them.

“A hoax call is a deadly and serious offense,” said Lt. Cmdr. Sara Wallace, chief of response at the Coast Guard division assigned to Maryland and the capital region.

She said nautical false alarms “not only put our crews at risk” but also endanger members of the public. “Our efforts to respond to what may be a hoax can delay us from getting on scene to a real emergency,” she said in a statement.

According to the Coast Guard, the most recent calls, made on a voice radio channel, were received Thursday at 10:27 p.m., and Friday at 1:08 a.m.

In a recording of one of the calls, a male voice can be heard intoning “Mayday, mayday, mayday.”

The voice is largely flat and expressionless.

At first, Wallace said, the Coast Guard sent searchers in response to the distress calls. But in time, she said, officials came to recognize the caller’s voice.

Nevertheless, the maydays were not ignored. Instead, Wallace said, several listeners were enlisted to reach a group decision as to whether the maydays came from the hoax caller and whether it was necessary to mount a search.

“Several people listen,” Petty Officer 3rd Class Jasmine Mieszala said, “to make sure” the Coast Guard is “not making a wrong decision in not launching” rescue vessels or aircraft.

In a statement released Friday, the Coast Guard estimated that the cost of searches prompted by the hoax calls has amounted to about $500,000.

At first, the Coast Guard said, monitoring equipment could indicate only that the calls came from somewhere along a line. Later, the service said, the number of apparent hoax calls prompted additional efforts to determine more specifically where the calls were coming from.

In its statement, the Coast Guard said making a false distress call is a felony with a maximum penalty of six years’ imprisonment, a $10,000 civil fine, a $250,000 criminal fine and re­imbursement to the Coast Guard.