The Fanno Creek Watershed, located within the Tualatin River Basin, covers over 20,000 acres, with about 4,500 acres within Portland city limits.  Fanno Creek flows in a westerly direction for about 15 miles from its headwaters in Hillsdale to its confluence with the Tualatin River near Durham.  Within the city, the primary land use is single-family residential housing, with very limited parks and open space.  The watershed contains steep slopes and mainly sandy clay loam soil.  Streets, parking lots, and building contribute to the large impervious surface area.  The narrow riparian corridors commonly consist of native species like western red cedar, douglas fir, vine maple, and swordfern, as well as invasive species like English ivy. Biological communities are limited, however, steelhead and cutthroat trout are present in upper Fanno Creek.