The pool's original deep blue color was caused by light scattering in deep, clear, hot water before vent obstructions altered its thermal dynamics.
The yellow and orange rings surrounding the pool are mats of thermophilic (heat-loving) bacteria that thrive in the cooler, outer edges.
In the past, visitors frequently threw coins into the pool, which acted as dams that disrupted the underwater plumbing and thermal convection.
Eruptions of nearby geysers can occasionally cause the water level and temperature of the pool to fluctuate temporarily.
The pool's temperature has historically fluctuated due to shifts in the underlying hydrothermal plumbing system.
Morning Glory Pool is a thermal feature in Yellowstone National Park characterized by its vibrant, multi-colored water caused by various species of thermophilic bacteria. The pool's name, given in 1883, references its resemblance to the morning glory flower. Historically, the pool was a deep, translucent blue, but human interference—including the tossing of coins, rocks, and trash—has partially clogged the vent, reducing water circulation and lowering temperatures. This cooling allowed orange and yellow bacteria to colonize the edges, shifting the color palette from deep blue to a blend of yellow, green, and orange. The pool is located at the end of the Upper Geyser Basin trail, requiring a hike from the Old Faithful area. It is a hydrothermal feature maintained by the National Park Service in its natural, albeit altered, state.
The elevated boardwalk view provides the best vantage point to capture the full circular shape and color bands of the pool.
Walk the boardwalk path from the Old Faithful area, as it provides a clear route through several other significant geysers.
Bring binoculars to get a better look at the color gradients and bacterial mats without leaving the designated boardwalk.
Visit during mid-morning or late afternoon to avoid the most crowded periods near the Old Faithful boardwalks.
Do not attempt to walk off-boardwalk; the ground is fragile and the thermal water is scalding.
Accessible only when park roads are open, typically from late spring through early autumn; winter access is limited to snowcoaches or guided snowmobile tours.
Stay strictly on designated boardwalks; never throw objects into the pool, as it damages the hydrothermal plumbing and water chemistry.
