The Montana Department of Transportation reports water has overflowed a ditch on Secondary Highway 308 between Red Lodge and Bearcreek.
The water is about 2 inches deep and covers about 40 feet of the road at mile post .3, the agency states in a news release.
Motorists should expect reduced speeds and single lane traffic in the area. Signs and cones have been set in place.
The water is expected to recede Tuesday night.