OKLAHOMA (NewsNation Now) — An Oklahoma mother lost her young son in June to open-air carbon monoxide poisoning while the family was spending the day on the lake. For Cassi Free, summer boating might be coming to a close, but her message is just ramping up.

Free says she hasn’t been back to the boat since her son died.

“It’s hard because this is where he spent the last day of his life,” said Free as she looked at the family boat.

Walking down the dock to it is just shy of impossible for her. But she climbs on board and untethers it —facing her grief in this way for the first time since June when her world lost its brightest little light.

“Andy had the time of his life all the time,” she said. “Just fearless, he always was.”

The youngest of three boys, Andy was her 9-year-old daredevil with a heart of gold. And he was a lover of the lake, so when family and friends set out on Oklahoma’s Lake Eufala at the onset of summer, it was another day of sun-kissed adventure.

“We had never been there. We launched, the kids went out. Everybody took turns tubing,” she said.

Six hours later, it was time to head home. The adults were in and out of the boat, packing up the car. The kids — avoiding chores to soak up the last moments on board.

“They said that the boat rocked, and Andy just rolled,” said Free. “By the time I got to the ramp, my husband was running up to get me and he was like Andy’s gone. I didn’t even know what he meant.”

For half an hour, paramedics performed CPR on Andy while the ambulance drove to the hospital. Emergency room nurse Brandi Jones took over when Andy arrived.

“One of the worst encodes that you can get is that there’s a baby on the way,” said Jones. “I can’t remember how many rounds, but with an adult, it usually doesn’t’ last that long. And, of course, with children, you want to go until parents say ‘please stop.’”

Andy was pronounced dead at the hospital, but it was still unclear what had happened. When Free’s two older sons started to complain about dizziness and exhaustion, she attributed it to trauma.

“And somebody was like well maybe they’re not tired, maybe they’re not finicky. Maybe they have carbon monoxide poisoning,” Free said.

Two tests and a medical examiner’s report confirmed that quickly — open-air carbon monoxide poisoning in all three boys. Andy’s levels of the gas were off the charts.

According to a report by the U.S. Coast Guard, carbon monoxide poisoning ranks fifth in the top five known causes of death among boaters; however, even the Frees, who have lifelong experience on the water, had no idea.

“I think that every boat launch, every marina, every dock needs to have a sign,” said Free.

She is now using Andy’s loss to warn others of the dangers lingering at the back of the boat. Preaching not to live in fear, but in facts — nobody can handle hours of engine exposure.

“I love him. I love him so much, and I’m sorry and I’m just so so proud of everything he accomplished,” she said. “And then I’d probably tell him to stay out of trouble in Heaven.”

So often on the water, people attribute feeling sick with too much sun, activity, maybe what we’re eating and drinking. Hardly do we ever think it could be a poisonous gas coming from the engine. Nurse Jones stressed avoiding sitting at the back of the boat all day long and making a cognizant effort to get fresh air even if you feel fine. Parents, of course, should also pay close attention to what their little ones are saying and feeling.