Sapphire Spring is a natural hot spring located in the Yellowstone National Park in the United States. Known for its stunning blue color, the spring is a popular attraction for visitors. The vibrant hue is due to the presence of thermophilic bacteria and minerals in the water, which create a beautiful contrast against the surrounding landscape. The spring has a temperature that can reach up to 200°F (93°C), making it one of the hottest springs in the park. It is part of the Yellowstone Caldera, a volcanic system that contributes to the geothermal features found throughout the area. Visitors are advised to stay on designated paths to protect the delicate ecosystem.