Firehole River

The Firehole is a small geyser-fed river that runs entirely within Yellowstone National Park, flowing about 21 miles north from the Madison Plateau through the Upper, Midway, and Lower Geyser Basins before joining the Gibbon at Madison Junction to form the Madison River. It is the most unusual trout stream in the Lower 48 — thermal inflows from hot springs and geysers raise the water temperature well above what trout normally tolerate. The result is a river that's too warm to fish for most of the summer but produces concentrated insect activity during the short spring and fall windows when temperatures drop into the fishing range.

It fishes as a meadow stream in slow runs and weed beds between the geyser basins. Walk-and-wade only, fly fishing only, almost entirely catch-and-release for rainbow and brown trout. The signature hatch is the White Miller caddis (Nectopsyche) — found in vast numbers almost nowhere else — along with PMDs, BWOs, and midges. Fish average 10-14 inches with occasional larger browns; the draw isn't trophy fish but the experience of casting to risers in front of erupting geysers.

Seasonal access is unusual. YNP opens the river on the Saturday of Memorial Day weekend (late May) and it fishes well through early July. As summer heat and geothermal input push water temps above 70°F, fishing slows dramatically and the river effectively closes itself by mid-July through Labor Day. It opens again in September with cooler weather and continues into the Park closure on the first Sunday of November. A YNP fishing permit is required — Wyoming state license is NOT valid in the Park. West Yellowstone, MT is the standard base camp, with Blue Ribbon Flies, Madison River Outfitters, and Bud Lilly's all within five minutes of the Madison Junction entrance.