Draining a rugged watershed of 2,462 square miles (6,380 km2), the river has an average flow of over 5,600 cubic feet per second (160 m3/s), accounting for a third of the discharge from the Clearwater basin.

The river immediately flows southwest through a narrow gorge, joined by numerous small tributaries.

Then it turns sharply west into a wider valley, where it receives its largest tributary thus far, 25-mile (40 km) Kelly Creek,[4] from the left near an unincorporated community, and turns west and southwest, paralleled by Forest Service Road #250.

Still narrow and winding, following the river's original course, the reservoir branches to the south and spreads wider as it enters more gradual terrain.

[5] The North Fork Clearwater's watershed covers 2,462 square miles (6,380 km2) of land in the lower Idaho Panhandle.

The logging industry makes up the primary economy of the North Fork's watershed.

In that time period, the highest recorded flow was 100,000 cubic feet per second (2,800 m3/s) on December 23, 1933.