The Firehole River starts south of Old Faithful, runs through the thermal areas northward to join the Gibbon and form the Madison River. The Firehole is world famous among anglers for its pristine beauty and healthy brown, brook, and rainbow trout.

Firehole River Canyon in Yellowstone N.P. is a great place to spend a few hours and get a respite from the desert sun. It includes rapids emptying into a deep pool as well as shallow sections outside the current. All should be careful to keep out of the main current.* The water is warm for this elevation because the river contains the runoff from many thermal features, including Old Faithful. Portable toilets are available (as of summer 2001). Camp at Madison campground near Madison Junction near the West Yellowstone entrance in order to be near the swimming. Courtesy of swimmingholes.org

The river is surrounded by geothermal features which empty water into it, which in turn affects the temperature of the water. Temperatures in the river have been measured as high as 86 °F and average 9 to 18 °F higher than areas upstream of geothermal influence. It is always good to discuss the water temperatures with a local park ranger to make sure temperatures are safe. 

*WARNING: All should be careful to keep out of the main current - A GIRL DIED HERE IN 2003 JUMPING INTO THE CURRENT AND GETTING TRAPPED UNDER AN OVERHANGING ROCK - DON'T DO IT.) Courtesy of swimmingholes.org

Check https://www.nps.gov/yell/planyourvisit/swimming-soaking.htm for closures, regulations, and conditions.