New Smyrna, FL – Police said two people were found dead on a boat on Disappearing Island off New Smyrna Beach on Sunday.

Coast Guard Petty Officer Christopher Evanson said 911 dispatch reported that a man and woman were found dead at about 11 a.m.

The victims were a couple from Palatka identified as 50-year-old Howard Lupton and 48-year-old Sandra Lupton. Evanson said both deaths are believed to be related to carbon monoxide poisoning.

Others celebrating the Fourth of July holiday on the water were stunned to see rescuers trying to revive someone on a boat.

Disappearing Island near New Smyrna Beach is a popular destination for boaters, and despite overcast skies, it was still packed on Sunday.

Some said the sight of the rescue attempt was disturbing.

“It was a little bit scary, because I was like, ‘Oh my God, what happened?'” said witness Yadara Rivera.

Officials said the couple was camping out in their boat overnight. Their son and his fiancé were in another boat nearby.

It was the son who found his parents, police said.

“In the morning, the son went over to check on the parents and they were not responsive, so they called for emergency help,” said Joy Hill, of the Florida Fish and Wildlife Conservation Commission.

Hill said a witness told them that the couple was running a generator overnight to keep the cabin of the boat cool.

An autopsy will be performed on Tuesday.