The hot weather contributed to 20 people being transported to a medical tent and one person to hospital during Sunday's race and half-marathon in Montreal, Urgences-Santé said.
The condition of the runner who went to hospital is not being made public.
Ten ambulances were deployed along the race route and firefighters sprayed runners with water to help them beat the unseasonable heat.
Medical director for the Rock 'n' Roll Oasis Montreal Marathon, Dr. François De Champlain, said hot days strain runners. The medical team saw people suffering from cramps, dehydration and even some runners collapsing after reaching the finish line, he added.
In total, about 900 people were evaluated by medical services along the route for a variety of different reasons, with the vast majority not requiring further attention. Organizers say this is not uncommon.
The unseasonably hot weather led to the cancellation of the 42.2-kilometre Rock 'n' Roll Oasis Montreal Marathon but the half-marathon, a distance of 21.1 km, and other races still took place this weekend.
The half-marathon started at 7:30 a.m., an hour earlier than previously scheduled, to avoid the hottest time of day.
21 km in about an hour
The half-marathon was won by Kenyan Daniel Gekara with a time of one hour, seven minutes and 56 seconds.
Ethiopians Dadi Beyene and Wendimu Adamu were right behind him, crossing the finish line 10 and 20 seconds later respectively.
About 14,500 people ran in the half-marathon. About 30,000 were registered for one of the races this weekend before the marathon was cancelled.
Several sections of roads downtown and around Parc La Fontaine closed Sunday including:
- De la Commune Street.
- Notre-Dame Street East.
- Amherst Street.
- Ste-Catherine Street.
- De Maisonneuve Boulevard.
- St-Hubert Street.
- Berri Street.
A complete list is available here. Some street closures may have changed with the cancellation of the full marathon.