The Firehole River flowing through Yellowstone National Park.
The Firehole rises in tiny Madison Lake which lies in a marshy subalpine basin at 8,200 feet along a north-facing slope of the continental divide. From the lake to the bridge on the Old Faithful-Thumb road under which it passes, this is a tiny, cold, winding brook trout stream that also holds a few pan-size browns.
Below the Old Faithful water supply intake, down to the bridge above Biscuit Basin and the mouth of the Little Firehole, is a two- or three-mile stretch that is currently closed to fishing. It never was really good fishing water, except for small spot locations, such as just behind Old Faithful and near Morning Glory Pool. Its closure, to protect the many thermal features, is a very small loss for the fisherman.