[4] By the time of Washington Territory surveys by Governor Isaac I. Stevens in 1853, the name had been translated to Bitterroot River.

[2] The Bitterroot Valley averages 7–10 miles wide and is uniquely low gradient for western Montana streams.

[2] The watershed is a snowmelt dominated system with large interannual variations in streamflow and peak flows from mid-May to mid-June.

[7] The variation is compounded by extensive irrigation withdrawals and upstream reservoir storage at Painted Rocks Reservoir on the West Fork Bitterroot River with the most severely dewatered reaches along 12 miles (19 km) of the river located between Woodside Crossing near Corvallis and Bell Crossing near Stevensville.

[9] Lolo Creek is often completely dewatered in late summer in its lower 2 miles (3.2 km) due to withdrawals for irrigation and rural water use.

In Montana, rainbow trout are only native to the upper Kootenai River in the state's extreme northwest corner.