Emerald Spring

The vibrant green color of Emerald Spring is caused by billions of thermophilic (heat-loving) algae thriving in the warm water. The water itself is actually a clear, deep blue, but the yellow sulfur and green algae combine to create the striking emerald hue. This natural optical illusion is a hallmark of the thermal features in Yellowstone.

Emerald Spring is located in the Back Basin area of the Norris Geyser Basin. Norris Geyser Basin is the hottest and most volatile thermal area in Yellowstone, sitting near the center of the park. The spring is easily accessible via the wooden boardwalks that wind through the basin.

The water temperature in Emerald Spring hovers around 154°F (68°C), which is relatively cool compared to Yellowstone's boiling geysers. This slightly lower temperature is exactly what allows the colorful thermophilic algae to survive near the edges. The water level and slight bubbling are fueled by escaping volcanic gases.

The USGS officially recognized the name Emerald Spring in 1930, though it had been informally named by earlier park superintendents. Early explorers and visitors were captivated by its distinct color, leading to its official incorporation into park maps. It has been a prominent highlight of Yellowstone's thermal tours for decades.