The Lucky Peak Fire was reported shortly after 9:00 a.m. It has burned 25 acres across the highway from the Spring Shores Marina.
Boise's Bureau of Land Management spokesman, Kevin Moriarty says fire crews had a hard time attacking the fire when it first began.
"It was on steep terrain, which is always difficult to try and control for firefighters," Moriarty told KBOI. "You usually have to use hand crews at that point, and they also had to boat across to it on the river, so access to it was very difficult."
Two helicopters and two planes helped get the flames under control by dropping retardant on the fire for a couple of hours.
Also fighting the fire were two 20-person crews and two engines from the Forest Service, one dozer and a fire investigator from the BLM, and two engines from Idaho Department of Lands.
BLM says that they were able to knock down the fire quickly because of the cooperation from different agencies.
Moriarty says the two hand crews will continue working to get the fire controlled through the night.
At this point, BLM doesn't expect traffic on Highway 21 to be impacted.