The Clackamas River begins on the slopes of Olallie Butte and flows 82.7 miles from its headwaters (elevation 6,000 feet) to its confluence with the Willamette River near Gladstone and Oregon City (elevation 12 feet) and is made up of 34 sub watersheds. The watershed drains more than 940 square miles or 600,700 acres. More than half of its length it runs through forested areas over rugged terrain. The lower reaches flow through agricultural and densely populated areas. The watershed crosses two counties and includes federal land administered by the US Forest Service and BLM, state land, and private land.

The Clackamas River Basin contains a municipal water source for approximately 300,000 people and watersheds that support significant wild runs of anadromous salmon.  It is home to the last significant run of wild late winter Coho in the Columbia Basin, and it is also one of only two remaining runs of spring Chinook in the Willamette Basin. In addition, it supports a significant population of winter steelhead. 

72% of the watershed is publicly owned, 3% is tribally owned, and 25% is privately owned. The watershed can roughly be divided in half, with nearly all of the upper watershed in the Mt. Hood National Forest and managed by the USFS. In contrast, most of the lower watershed is privately owned. The area in between the national forest and the lower watershed includes parcels of land owned by private timber companies and the BLM.