Courtesy photo Lady Michigan crew member Matt Southwell fights a fire on a boat the eventually sank in Thunder Bay on Friday.

ALPENA — Emergency crews responded to a boat on fire in Thunder Bay far off the Alpena shoreline Friday afternoon.

The blaze injured a pair of area residents and the boat — which officials said appeared to be an 18 to 20-foot pleasure craft — eventually gave way to the damage received by the blaze and sank.

It is not known at this time what caused the fire.

A press release from the Alpena Fire Department said two people were treated by a private boater, who was an off-duty firefighter paramedic from Green Bay, Wisconsin. The good Samaritan transported the victims to Alpena aboard his boat to meet the city’s first responders.

Alpena paramedics continued treatment of a 55-year old man with burns and a woman with less severe injuries. Both patients were transported to MidMichigan Medical Center-Alpena.

Alpena Fire Chief Bill Forbush said the passengers were local residents.

The Alpena Sheriff’s Department, the U.S. Coast Guard, and Michigan Department of Natural Resources responded to the fire.

Lady Michigan, which provides shipwreck tours in Lake Huron, used its fire suppression system to help extinguish the blaze, but to no avail as the boat eventually dipped beneath the water’s surface.

Lady Michigan Captain Spencer Cootware, who is in the Coast Guard Auxiliary out of Naples Florida, said there was a boat full of tourists on board when he heard the mayday call from the distressed boat. He contacted the Coast Guard, offered assistance and was asked to lend a hand. He said he brought Lady Michigan up alongside the burning boat and 1st Mate Matt Southwell used a firehouse to fight the fire.

“I heard someone come over the radio and say ‘mayday, mayday, we’re on fire,'” he said. “It came across the radio really loud, so I knew they were close. We fought the fire for about 25 or 30 minutes before it finally sank.”

Cootware said the boat sank in about 30 feet of water.

Lady Michigan’s crew is trained to handle many emergencies, Cootware said, and there are procedures listed on the glass-bottom boat that outline what to do if the need to help someone arises.

The 911 call came in at 2:11 p.m. and reported a boat was on fire near Sulphur Island. The boat was well north of that spot when first responders arrived at the small boat harbor.

Dozens of onlookers watched the fire unfold from the breakwall, with some believing it was a freighter because of the size of the smoke plume that turned the blue afternoon sky black.

Officials say it was not a freighter.

Alpena County Undersheriff Erik Smith, who was on the county’s water rescue boat at the scene, said the boat on fire appeared to be a pleasure craft in the 18 to 20-foot range. He added the boat was already severely damaged when he arrived at the scene, which made it difficult to determine its exact size.

Cootware said he believed it was about between 20 and 30 feet long.

Southwell said the episode was odd, because as the tourists learned about the shipwrecks on the tour, and told them many of them sank because of fire, they got to see one burn and sink in person.

“They definitely got their money’s worth,” Southwell said.