SANDPOINT — A collision on Priest Lake is highlighting the risks of carbon monoxide poisoning while boating.

Two boaters were stricken while fishing and crashed into a docked sailboat at Kalispell Bay on March 13.

Bonner County Sheriff Marine Patrol Supervisor Lt. Cary Kelly said the two men from Spokane, Wash., started fishing at about 8 a.m. in blustery conditions. The wind was too strong to use the electric trolling motor, so they used the boat’s main engine, a 50-horsepower Evinrude.

To keep warm, they fired up a propane gas-powered space heater and used the boat’s rain cover for shelter, Kelly said.

Between the exhaust from the outboard and fumes from the heater in the enclosed space, the two were sickened but apparently managed to stay semi-conscious, according to Kelly.

Shortly after 4 p.m., an eyewitness watched the 20-foot Crestliner slam into the unoccupied sailboat near the Linger Longer Lodge. Kelly said the powerboat drifted for a couple hundred feet before its 31-year-old operator could restart the engine.

The fishermen left the area without telling anyone of the collision, loaded the boat onto their trailer and returned to Spokane.

“After 12 o’clock they had no memory of events — including how they got home from Priest Lake,” said Kelly.

The eyewitness noted the registration numbers on the boat’s hull and license plate numbers of the trailer and the vehicle that was towing it. Sheriff’s officials quickly tracked the men down, although they were still unaware they had been in a collision.

The fisherman who was at the helm of the boat later received medical attention at a hospital, where he was placed on oxygen and underwent a carboxyhemoglobin exam. Kelly said doctors suspected carbon monoxide poisoning.

“We were going to cite him for negligent operation until we substantiated the fact that they really didn’t know what they were doing,” said Kelly.

The damage to the motorboat was estimated at $9,000. The damage to the 24-foot sailboat was estimated at $2,000.

Carbon monoxide — a toxic gas that’s odorless, tasteless and non-irritating — can cause headaches, flu-like symptoms and death.

Kelly said carbon monoxide poisoning is often an underestimated risk while boating. A growing body of research is indicating that drownings in areas where boats operate are attributable to carbon monoxide poisoning.

A spate of deaths on houseboats on Lake Powell in the southwest has drawn attention to the risks.

The BoatUS Foundation recommends turning off engines and generators while swimming near boats. Carbon monoxide detectors are also recommended on boats with enclosed cabins.

“All you need is a few gulps of it to make you pass out,” said Kelly. “It can be dangerous very quickly.”