North Summit Fire District Battalion Chief Tyler Rowser said the man fell while reaching for a fishing pole around 9 a.m. He was not wearing a life jacket.
He said others in the same boat were unable to get the fisherman out of the water, but hailed a passing watercraft for help.
The second boat pulled the fisherman from the reservoir and took him to the Red Rock Campground boat launch. He was taken by medical helicopter to a Salt Lake Valley hospital in critical condition, the battalion chief said.
The man’s name was not released.
It wasn’t immediately clear how long the fisherman was in the water. A current conditions report on the state parks website indicates the water temperature at the Coalville-area reservoir was 59 degrees.
Rowser said anyone recreating on the water should wear a flotation device and understand that the water will be very cold, especially at this time of year.
A spokesman from the Department of Natural Resources’ Division of Law Enforcement said the agency is investigating the incident.