The Firehole River, first discovered in the 1830s, is one of two major tributaries of the Madison River. It joins the Gibbon River at Madison Junction to form the Madison River. From its source at Madison Lake to its confluence with the Gibbon, the Firehole River flows north for just over 20 miles. It is home to three Yellowstone waterfalls, Kepler Cascades, Firehole Falls and Cascades of the Firehole. While once fishless above Firehole Falls, the Firehole River is today an excellent fly fishing hole. Sound humdrum? Wait, there's more! The Firehole River flows through three major geyser basins, Upper Geyser, Middle Geyser and Lower Geyser basins. By the end of its run, nearly one quarter of the river's water comes from hot bubbling geothermal features. The runoff from hot springs and geysers increases the temperature of the water and changes the ecology of the river.