Two brothers were found dead on a boat Saturday morning after authorities said they spent the night on Lake Lanier but left a generator running.

The men’s bodies were discovered by friends and family members about 11 a.m. in Bald Ridge Creek near Mary Alice Park, Forsyth County Sheriff’s Office spokeswoman Stacie Miller said.

According to investigators, three men spent the night aboard a cabin cruiser that was anchored in the lake.

“It is believed that they were running a generator all night with the canopy of the boat closed,” Miller said, adding that carbon monoxide poisoning is the suspected cause of death.

Though the generator was located in an area of the boat that was not enclosed, its positioning did not allow the exhaust to exit the boat, she said. Instead, the toxic fumes filled the cabin as the men slept.

The men were identified Saturday as 22-year-old Scott Landeck and his older brother, 31-year-old Brian Landeck. Both lived in Cumming, deputies said.

Family members were able to wake the third man when they found the boat Saturday morning, but he was disoriented, officials said. The vessel was driven to Mary Alice Park, where they met with first responders.

Officials called the deaths a “tragic accident,” and encouraged boaters to be careful when using generators by ensuring they are positioned in a way that allows for adequate ventilation.