Boulder Creek is a popular whitewater river in Idaho, known for its exciting rapids and beautiful scenery. The ideal streamflow range for Boulder Creek is between 200 and 800 cubic feet per second (cfs), with the highest flows occurring in late May and early June. The river is classified as a Class III to IV, meaning it has moderate to difficult rapids with high waves and narrow passages.

The segment of Boulder Creek used for whitewater rafting is 6.5 miles long, starting at the Boulder Creek Trailhead and ending at the South Fork of the Payette River. This stretch of river features a variety of rapids and obstacles, including Boulder Drop, a popular Class IV rapid with a steep drop and large waves.

There are specific regulations in place for whitewater rafting on Boulder Creek. All river users must obtain a permit from the Boise National Forest, and commercial outfitters are required to have a special use permit. Additionally, all rafters must wear a Coast Guard-approved personal flotation device (PFD) and helmets are strongly recommended.

In summary, Boulder Creek is a thrilling whitewater river in Idaho with an ideal streamflow range between 200 and 800 cfs. The 6.5-mile segment is classified as Class III to IV, featuring exciting rapids like Boulder Drop. Specific regulations and permits are required for rafting on the river to ensure safety for all users.