Southeast of Columbia Falls, the Middle Fork of the Flathead River is known wild cutthroats. The river starts just outside the Great Bear Wilderness Area, flows through deep gorges in the wilderness area, exits the wilderness near Essex and then merges with the North Fork near West Glacier. Near Essex, the river is paralleled by SR2 to West Glacier and this offers many access points.
Like the North Fork, this is not a big fly fishing river, so dont expect to find trophy trout, except in the Wilderness section where cutthroats grow to 16 inches.
Note: Bull trout may cruise these waters and it is illegal to intentially fish for them.
Overall, Middle Fork Flathead River is the 5th most popular fly fishing river of all 21 fly fishing spots in Montana.