Emerald Spring is a hot spring located in Norris Geyser Basin of Yellowstone National Park.
Originally named Emerald Geyser by Philetus Norris, park superintendent (1877–1882) because of its color, the name was later officially changed to Emerald Spring by the U.S. Geological Survey in 1930. Emerald Spring is 27 feet (8.2 m) deep. The water temperature in the spring is around 83.3 °C (181.9 °F).
The spring gets its name from the emerald green color of the water created by sunlight filtering through the water, giving the light a blue color, and reflecting off the yellow sulphur creating the green hue.
While Emerald Spring is a mostly calm pool, which usually only has a few bubbles rising to the surface, it does experience periods of turbidity and small 3-foot (1 m) high eruptions. In 1931, Emerald experienced a period of extremely vigorous activity with eruptions measuing 60 to 75 feet (18.2–22.9 m) in height.