Harris Creek drains a broad upland terrace that features extensive wetlands as well as several lakes and ponds, including Lake Joy. From approximately RM 4 to RM 2, the creek flows through a steeper canyon section to the valley floor, before meandering for two miles through current and former agricultural lands within the Snoqualmie River floodplain. The final mile of the creek flows through the WDFW Stillwater Wildlife Area.

The uppermost reaches of the mainstem feature forestry as the primary land use, including both State-owned and private forest lands. The bulk of the sub-basin comprises rural residential land uses, entirely within unincorporated King County. The highest densities are found around the two largest lakes – Lake Joy and Lake Marcel, where most lot sizes range from 0.3-1.0 acre in size. Like many other tributary sub-basins, there are numerous small farms within the rural residential portions of the drainage. The entire sub-basin is served by on-site septic systems.

Stillwater Creek is the second major stream in the Harris Creek sub-basin. The creek flows into and out of Lake Marcel, before flowing through a canyon reach to the floodplain. Stillwater Creek joins Harris Creek just before it enters the Stillwater Wildlife Area.

The documented distributions of coho salmon and steelhead extend into the upper watershed where extensive wetlands and ponds likely provide excellent rearing habitat. Chinook salmon are presumed to utilize floodplain portions of the stream as juveniles, but spawning is not known to occur in Harris Creek. Coho salmon are also known to ascend Stillwater Creek as far as the Lake Marcel outlet.