File:Thermal image of Ledge Spring (late afternoon, 1 June 2017) 2.jpg

English: The temperature scale is in degrees Fahrenheit.

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Ledge Spring is a hot spring that has moderately rare geyser eruptions. It is located in the Lower Group of Yellowstone's West Thumb Geyser Basin. Its basin is irregularly quadriltateral in shape and is about 7.5 x 8.5 meters in size. The water level varies with time. When inactive, water levels are usually low. When active as a geyser, the basin is water-filled. Eruption water drains across a wide runoff channel heading southeast, then east, toward Yellowstone Lake.

Eruptions were first reported in 1928 and sporadically since then. In recent decades, Ledge Spring was active as a geyser in summer 1991, late summer 1996, mid-summer 1999, summer 2001, 2004, summer 2005, and mid-summer 2007. Ten years after that, Ledge Spring started having eruptions again in 2017. Observers reported evidence of eruptions in May 2017, once the West Thumb area opened after the annual winter-spring park closure. Eruptions have been witnessed in late May and June 2017. Current activity varies from heavy roiling to low doming to moderately low doming spouts, maybe up to a meter high at most. After eruptions, water level usually (but not always) drops below overflow. Between eruptions, water level slowly rises, resulting in trickling to slight overflow. Overflow cycles from somewhat heavy to moderately light. In the half-minute before an eruption, overflow is very heavy and the basin increases in steaminess. 2017 eruptions are brief, lasting less than a half-minute. Most eruptions occur every 20 to 30 minutes, but reported closed intervals (= eruption start to eruption start) have ranged from 11 minutes to 55 minutes.