Key points at a glance Key points at a glance. Original editorial diagram. An open deck feels like the safest place in the world to breathe. Wind, sky, water in every direction. It's easy to believe the exhaust just goes away. It doesn't always.
Quick answer: Yes. Carbon monoxide (CO) can reach people on open decks and pontoons, because every fuel-burning engine makes it, four-stroke outboards included. It builds up under swim platforms, between pontoons, near other running boats and when a tail wind blows exhaust back aboard. Know where your exhaust goes, brief passengers, treat headaches and dizziness seriously, and call 911 if you suspect poisoning.
Key points at a glance. Original editorial diagram.
An open deck feels like the safest place in the world to breathe. Wind, sky, water in every direction. It's easy to believe the exhaust just goes away.
It doesn't always. Carbon monoxide is an invisible gas made by fuel-burning engines and appliances. You can't see it and you can't count on smelling it. Transport Canada's 2026 Safe Boating Guide warns that it can be present in open deck areas, and it adds a line every pontoon owner should know: swimmers can be overcome by breathing CO and drown in minutes.
That covers every pontoon, tiller boat and fishing boat on Rice Lake, and it covers four-stroke outboards. A clean-running modern motor still burns fuel, so it still makes CO. The useful response is to know where the exhaust goes on your boat and to put it in your passenger briefing.
Where Does CO Build Up on an Open Boat?
Find out where your engine and any generator discharge their exhaust. Then think about where your people sit, wait to board and enter the water.
Transport Canada names the high-risk spots and situations:
- Under swim platforms and between the pontoons of boats and houseboats
- Two boats tied to each other, or a boat docked alongside a seawall
- Groups of boats trolling in one area
- A load that makes the bow ride high
- An engine or fuel-burning appliance running while the boat isn't moving
- A tail wind carrying exhaust back on board
None of that is limited to cabin cruisers. Use your boat's manual to find the actual outlets. A generic drawing can't show them all, and the motor you can see may not be the only fuel-burning equipment aboard.
Idling Isn't a Harmless Waiting Mode
The dock is busy. Somebody's sorting a line, a passenger is stepping aboard, another boat is waiting alongside. That routine moment is when exhaust gets a chance to collect.
The CDC explains that slow operation, idling, blocked exhaust and wind carrying exhaust back toward a boat can all let CO build up, including in open areas. Transport Canada's advice is to idle only in well-ventilated areas.
So:
- Don't run the engine or generator longer than you need to around people.
- Don't use the stern or swim platform as a waiting spot near running exhaust.
- Keep people out of the water near those areas.
- Never let anyone hold onto the platform of a moving boat.
No seat or distance is safe on every boat in every wind with every neighbour. If exhaust is reaching people, change the situation. Don't try to tolerate it.
On a Pontoon
Pontoons are our home turf, so this one's worth a minute. They feel wide open, which is exactly why people relax about this.
Transport Canada lists the space between pontoons as a high-risk area, because exhaust can get in there and sit. Add a rear swim deck or ladder with the outboard right beside it, plus a crowd waiting to climb aboard, and you have a spot where people gather close to the exhaust. Kids on the back deck while you idle at the dock is the picture to avoid.
Think through the same routine on your boat. Where does everyone stand when you pull up to the ramp? Who's at the back when the engine's running? Is anyone swimming off the back while it idles? If you've added a cover, enclosure curtains or a heavy load of gear, check again. The airflow you were used to may have changed.
Our guides on whether a pontoon is right for your family and common pontoon problems on Rice Lake cover the rest of owning one.
Make the Briefing Specific
A good briefing is short:
- Show passengers where the exhaust comes out on this boat.
- Tell them which stern and platform areas to stay clear of while an engine or generator is running.
- Ask them to speak up immediately if they feel unwell.
- Explain what a CO alarm means and who takes charge if it sounds.
Ask the person who boards from the stern what they usually do while they wait. Ask whoever's watching the swimmers how they'll keep track of everyone. Questions like these find the gaps that a general "be careful" never will.
If you change the boat's enclosure, load or equipment, redo the briefing.
Don't Write It Off as Seasickness
Headache, dizziness, weakness, nausea, fatigue and confusion can all be signs of CO exposure. Transport Canada notes they can easily seem like seasickness or the flu.
If you suspect CO poisoning:
- Get the person into fresh air right away.
- Call 911 or get emergency medical help.
- Tell the responders CO exposure is possible.
Don't wait for a second person to get sick. Don't send somebody into a space you think is contaminated to investigate. Getting help matters more than proving the cause.
Use the Right Alarm and Keep It Working
Follow the boat and alarm makers' instructions for marine CO alarms, including where to install them, how to test them and when to replace them. The US Coast Guard says never to ignore a CO alarm and to maintain both detectors and exhaust systems.
An alarm is an extra warning. It doesn't make an exhaust-exposed swim platform safe, and it doesn't replace good ventilation or sensible engine use.
What We See at HBW
A busy Rice Lake summer weekend is full of the moments this post is about: engines idling at the dock and the ramp, people climbing aboard, kids heading for the back of the boat. Everyone's watching the line or the ladder. Nobody's thinking about the exhaust. Fall walleye trolling adds one more, since Transport Canada lists groups of boats trolling in one area as a build-up risk.
Renting a pontoon for the first time? Our first-time rental guide covers the rest of the day.
If you aren't sure where your exhaust goes, bring the boat in. Our Rice Lake boating guide has the lake basics, and a service request at hbwservice.ca gets us started on the boat.
Before the next outing, find the outlets, read the boat's CO instructions and brief the people who use it. An open boat still needs an exhaust plan.
Sources
Not Sure Where Your Exhaust Goes?
Put in a service request and we'll take a look at the boat. In an emergency, call 911.
Phone: 905-342-2153
Service: hbwservice.ca
Configurator: mercuryrepower.ca
Address: 5369 Harris Boat Works Rd, Gores Landing, ON
