The Tryon Creek Watershed is divided into three subwatersheds:
Tryon Creek Mainstem
The Tryon Creek subwatershed is 3,083 acres. The mainstem of Tryon Creek is about sevem miles long from its headwaters near Multnomah Village (just north of Interstate 5 and Highway 99) to its confluence with the Willamette River in Lake Oswego at the Highway 43 crossing.
The Arnold Creek subwatershed is about 775 acres. Arnold Creek joins Tryon Creek at the Boones Ferry Road crossing.
The Falling Creek subwatershed is about 283 acres. Falling Creek joins Tryon Creek at SW 26th Avenue and Taylors Ferry Road. Other smaller tributaries flow into Tryon Creek both within and outside Portland's city limits.