Emerald Spring is a natural hot spring located in Yellowstone National Park, Wyoming. Known for its vibrant green color, the spring is formed by mineral-rich water that heats up underground and rises to the surface. The unique coloration is due to the presence of thermophilic bacteria that thrive in the warm water. The temperature of Emerald Spring can reach up to 160°F (71°C), making it one of the hotter springs in the park. Visitors are often drawn to its beauty, but swimming or wading is prohibited to protect the delicate ecosystem. The spring is part of the park's geothermal features, which include geysers and other hot springs.