The call came in at about 5 p.m near the Turner Gulch area.
BLM says the fire has grown to about 300 acres and is in an area that is making it difficult to get crews to.
Some crews were being ferried by boat across the reservoir to reach the fire.
Helicopters are also responding to help fight the fire.
No homes or structures have been threatened.
BLM officials expect crews to have the fire contained by 8 p.m. Tuesday.
The fire is believed to have been human caused.
More details will be reported as they become available.