The Whitewater River run in the Tatoosh Wilderness Boundary to Confluence with Clear Fork Cowlitz River is a popular destination for experienced whitewater enthusiasts. The ideal streamflow range for this section of the river is between 800 and 1500 cubic feet per second (cfs), providing a challenging yet manageable level of water flow for rafters and kayakers. The class rating for this segment is III-IV, with some Class V rapids present at higher water levels.

The segment mileage for this run is approximately 7 miles, starting at the Tatoosh Wilderness Boundary and ending where the Whitewater River meets the Clear Fork Cowlitz River. The river features several notable rapids and obstacles, including the S-Turn rapid, which can be challenging at higher water levels, and the Boulder Garden, which requires precise maneuvering through a series of large rocks.

There are specific regulations to the area that visitors should be aware of. The Tatoosh Wilderness is designated as a wilderness area, and visitors are expected to follow Leave No Trace principles to minimize their impact on the environment. Additionally, there are restrictions on campfires and certain types of equipment, such as chainsaws and motorized vehicles, to protect the natural habitat.