Emerald Spring, Hot spring in Norris Geyser Basin, Yellowstone National Park, Wyoming, United States.

Emerald Spring is a hot spring in the Norris Geyser Basin of Yellowstone National Park featuring deep green and blue colored waters. The colors come from dissolved minerals and heat-loving microorganisms that thrive in the warm environment.

Yellowstone National Park, where this spring is located, was established in 1872 as the first protected national park in the United States. This designation marked a turning point in preserving geothermal features for future generations.

Philetus Norris, park superintendent from 1877 to 1882, named the feature Emerald Geyser for its color; the U.S. Geological Survey officially changed the name to Emerald Spring in 1930. In 1892 physicist Robert W. Wood secretly dissolved a pint of fluorescein in the pool as a prank, startling witnesses with unusually colorful water.

You can reach this spring via wooden boardwalks built throughout the Norris Geyser Basin for safe movement around thermal features. Staying on marked paths keeps you safe and protects the delicate geothermal environment.

In 1892 optical physicist Robert W. Wood secretly dissolved a pint of fluorescein in the pool, turning the water an unnatural colour to surprise onlookers. The spring is usually a calm pool with a few bubbles, but in 1931 it erupted 18 to 23 metres high.