Is the Gulf of St. Lawrence rough? What to expect on the crossing
Yes, especially from October to January. In modelled data the average daily peak wave height is about 2.5 m in November and about 2.6 m in December, against about 1 m in July. In winter, ice can cover the sea, which stops waves forming but delays ferries.
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Gulf · Eastern Canada · Reputation among passengers: has a long-standing reputation for rough passages.
- Low
- Moderate
- High
- Very high
Roughness summarises typical reported conditions for this crossing, not a forecast for any given sailing.
Open gulf, autumn wind waves, winter ice
In the Nausea Index table of the 128 sea crossings we cover, the Gulf of St. Lawrence is rated rough, one of 38 in that band, with 6 rated higher. Full table: the roughest sea crossings, ranked.
Key facts
- The Gulf of St. Lawrence is a gulf, and passenger reports place it in the high roughness band.
- The mechanism behind that reputation: Open gulf, autumn wind waves, winter ice.
- Conditions are reported roughest in January, November and December.
- The calmest months are usually February, March, May, June, July and August.
- It is also known as Golfe du Saint-Laurent.
Why is the Gulf of St. Lawrence so rough?
The Gulf of St. Lawrence covers 226,000 km2 and averages 152 m deep, with a maximum depth of 530 m. In the Magdalen Islands the wind amplifies the coastal waves, which are most often 0.5 to 2 m high and break every four to seven seconds. Relais Nordik says that outside the high season the river enters a more active phase with more waves, and that November and December are windier months.
When is the Gulf of St. Lawrence roughest?
Relais Nordik says November and December are windier months, with more waves and a schedule that may be disrupted. Wikipedia says ice covers the entire gulf in January and February and prevents waves forming, and CTMA says its schedule changes are more frequent in winter, depending on weather and ice conditions. Modelled wave heights are highest from November to January and lowest from May to August. February and March show as calm only because the model has no wave value for 37 to 39% of their days, which this guide counts as zero; on the other days it averages about 2.45 m in February and 2.25 m in March.
| Roughest water in Jan | Roughest water in Feb | Roughest water in Mar | Roughest water in Apr | Roughest water in May | Roughest water in Jun | Roughest water in Jul | Roughest water in Aug | Roughest water in Sep | Roughest water in Oct | Roughest water in Nov | Roughest water in Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Roughest | Calm | Calm | Mixed | Calm | Calm | Calm | Calm | Mixed | Rough | Roughest | Roughest |
Typical seasonal pattern, not a forecast. Any month can deliver a calm crossing or a bad one. Check the marine forecast for your sailing date. Select a month to see every sea and ferry crossing ranked for it.
Month bands: Dizzout sea-state data for Gulf of St. Lawrence, built from the reports and sources listed at the foot of this page. Free to cite with a link to this page.
Where to be on board
Front to back
- Bow (front)Avoid
- MidshipBest
- Stern (aft)OK
The crossing: 1 hour to 7 days
Roughest stretch: Open water between Prince Edward Island and the Magdalen Islands
Sit low and near the middle of the ship, or book a cabin. Waves here are short, so the upper decks and the ends move more.
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The crossings that cross it
| Route | Typical duration | What to know |
|---|---|---|
| Souris (Prince Edward Island) to Cap-aux-Meules (Magdalen Islands) | 5 hours | CTMA ferry Madeleine II. Schedule changes are more frequent in winter, depending on weather and ice conditions. |
| Cap-aux-Meules to Île d'Entrée | About 1 hour | CTMA ferry within the Magdalen Islands. |
| Rimouski to Blanc-Sablon and back | Usually 7 days, depending on the weather conditions | Relais Nordik's Bella Desgagnés, a cargo-passenger ship that stops at Sept-Îles, Port-Menier on Anticosti Island, Havre-Saint-Pierre and other north shore villages. |
What helps on this crossing
- Book a cabin for the five-hour Magdalen Islands crossing if you can. CTMA lists 15 cabins on the Madeleine II.
- Pick May to August if you can. Modelled wave heights are lowest then, and Relais Nordik says the off-season, such as November, may not suit anyone very sensitive to seasickness.
- Sign up for CTMA's alerts. It sends a telephone, text or email notice when weather delays a crossing.
- Dizzout, a drug-free sound therapy app for passengers: it works with any headphones once nausea starts, with relief in about 90 seconds.
For the full toolkit see the seasickness guide, or what to do once it has already started. For what the trials actually say about the oldest trick on that list, see the verdict on looking at the horizon. If the rocking follows you ashore afterwards, that is land sickness, which is normal, and it passes.
Frequently asked questions
Is the Gulf of St. Lawrence rough in November?
November is one of the roughest months. Relais Nordik says November and December are windier, with more waves, and that its schedule may be disrupted. In modelled data the daily peak wave height near the Magdalen Islands averages about 2.5 m in November, against about 1 m in July.
Is the Gulf of St. Lawrence rough in July?
July is the calmest month in the same data, with the daily peak wave height averaging about 1 m near the Magdalen Islands. CTMA also says schedule changes are more frequent in the peak travel period, from June to September, but it does not give the reason.
How long is the ferry to the Magdalen Islands?
CTMA calls it a five hour crossing between Prince Edward Island and the Magdalen archipelago, aboard the Madeleine II. A second CTMA ferry, between Cap-aux-Meules and Île d'Entrée, takes approximately 1 hour.
What are the waves like at the Magdalen Islands?
Wikipedia says the wind amplifies the coastal dynamics there, with waves most often 0.5 to 2 m high breaking on the coast every four to seven seconds. That is a short-period pattern, and it describes the coast, not the open water of the crossing.
Is the Gulf of St. Lawrence rough in winter?
Often, for part of it. In a typical year, December is rated roughest, January roughest and February calm. This is the typical pattern, not a forecast for any sailing.
Other crossings
Sources & further reading
- https://en.wikipedia.org/wiki/Gulf_of_Saint_Lawrence
- https://en.wikipedia.org/wiki/Magdalen_Islands
- https://www.traversierctma.ca/en/
- https://www.traversierctma.ca/en/discover-our-ship/services-on-board
- https://www.traversierctma.ca/en/discover-our-ship/technical-data
- https://www.traversierctma.ca/en/before-departure/faq-en
- https://www.traversierctma.ca/en/other-services/the-cap-aux-meules-ile-d-entree-ferry
- https://www.relaisnordik.com/en/
- https://relaisnordik.com/en/itineraries-and-stopovers/
- https://relaisnordik.com/en/off-season-travel-on-the-bella-desgagnes/
- https://open-meteo.com/en/docs/marine-weather-api
- https://marine-api.open-meteo.com/v1/marine?latitude=47.5&longitude=-62.0&start_date=2015-01-01&end_date=2024-12-31&daily=wave_height_max&models=era5_ocean&timezone=GMT
Sea conditions described here are typical patterns drawn from published marine and operator information as of July 2026, not a forecast: conditions on any given sailing depend on the weather that day, and any month can deliver a calm crossing or a bad one. Route and operator names are trademarks of their respective owners; Dizzout is not affiliated with or endorsed by them. Seasickness sensitivity varies from person to person; this page is informational and not medical advice.