Athletes compete in the first IRONMAN Canada-Ottawa on Sunday, Aug. 3, 2025. More than 2,500 participants took on the gruelling course, which featured a swim in the Ottawa River, a bike ride through urban and rural scenery and a run through downtown. Photo by Ashley Fraser /Postmedia

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Ottawa will be buzzing this Colonel By Day long weekend as more than 3,000 athletes from 65 countries descend on the national capital for the second Ironman Canada-Ottawa, causing major road closures across the region.

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The long-distance triathlon begins Sunday morning with a swim at Britannia Beach before competitors cycle through Ottawa and Gatineau and finish with a marathon through the downtown core.

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Monday marks Colonel By Day, known elsewhere as the Civic Holiday, with many attractions and businesses remaining open, while some city services take the day off.

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Here’s what you need to know before heading into this long weekend.

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The race begins at 6 a.m. Sunday with a 3.8-kilometre swim at Britannia Beach, followed by a 180-kilometre bike ride and a 42.2-kilometre marathon. Athletes have up to 17 hours to complete the course.

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The first athletes are expected to cross the finish line at Major’s Hill Park around 2 p.m., while the final competitors have until about midnight to complete the race.

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The finish-line celebration, known as Magic Hour, runs from 10 p.m. to midnight Sunday.

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The race starts at Britannia Beach, with the bike course then traveling through Britannia, downtown Ottawa, Blackburn Hamlet, Gatineau and Mooney’s Bay before athletes transition from their bikes to the run at the National Gallery of Canada. The race finishes at Major’s Hill Park.

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The marathon will take runners past Parliament Hill, along Queen Elizabeth Driveway and through the Central Experimental Farm before finishing at Major’s Hill Park beside the National Gallery of Canada, with views of Parliament Hill.

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Road closures begin as early as 3 a.m. Sunday, and some streets may remain closed until about 1 a.m. Monday.

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Major roadways affected include:

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Bridge closures include:

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OC Transpo routes along the Ironman race course will be detoured Sunday. On Monday, Colonel By Day, buses will operate on a Saturday schedule. Riders are encouraged to check OC Transpo’s website before travelling.

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The Royal Canadian Air Force will perform two fly-overs during the Ironman schedule: