About 3,000 people are expected to take part in the Vermont City Marathon in Burlington.
The race starts at 8 a.m. on Sunday and temperatures are expected to rise into the 80s throughout the day.
RunVermont is planning additional relief efforts. Misting stations, ice drops and roving "ice patrols" were expected to be added to keep the runners cool.
Organizers also are increasing water stacks by about 15 percent and expanding the race's official time limit from six hours to six-and-a-half hours.
New runners who are only running a section of the course were encouraged to start early.
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