Temperatures in the river have been measured as high as 30 °C (86 °F) and average 5 to 10 °C (41 to 50 °F) higher than areas upstream of geothermal influence.

All these tributaries bring cool waters to the Firehole and provide refuge for trout in the mainstem during mid-summer high temperatures caused by geothermal activity.

By the late 19th century, the Firehole and Yellowstone National Park in general was a popular destination for fishermen.

In 1955 all stocking programs in the park were discontinued and today's Firehole trout are completely wild populations.

In 1968, based on increasing pressure on the Firehole, the Gibbon and Madison rivers, the National Park Service designated these waters as Fly Fishing Only.