Grand Prismatic Spring Overlook is one of the Yellowstone National Park’s newer trails, built to protect the spring and provide a great point from which to observe this fascinating phenomenon. The trail shares the trailhead with the Fairy Falls Trail. The wide and flat crushed gravel trail starts at the bridge crossing the Firehole River. It continues gently up through the regrown lodgepole forest until you arrive at the spacious viewing platform. The view of the Excelsior Geyser and Grand Prismatic Spring is spectacular. The Grand Prismatic can reach a temperature of 188°F and is the hottest at the blue waters at its center. The color turns green away from the center, where the temperature is 165°F degrees, as a result of Synechococcus bacteria. At the outer rim of the spring, Calothrix and Phormidium cyanobacteria turn the water orange and dark brown.

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