Brilliant Pool, Hot spring in Yellowstone region, Teton County, US.

Brilliant Pool is a hot spring in the Upper Geyser Basin of Yellowstone National Park, part of the Daisy Group. It is connected underground with Daisy Geyser and Splendid Geyser, and its water level rises and falls with their eruptions. When the pool drops low enough during a sustained series of Splendid eruptions, it erupts on its own for a few seconds at a time.

The hot spring formed thousands of years ago through intense volcanic activity and underground magma movement that shaped the Yellowstone landscape. The geothermal area evolved over time as fractures and cracks in the rock created new paths for heated water to surface.

The pool's behaviour is watched by geyser gazers who time Daisy and Splendid eruptions by its water level. When Daisy erupts, the pool drops a few inches and refills as Daisy refills; a Splendid eruption lowers it further. In the early 1950s the pool overflowed for a phase, and Daisy stayed dormant until the pool returned to normal.

Brilliant Pool sits in the Daisy Group of the Upper Geyser Basin, reached on foot by the basin's boardwalks. Watch the water level: it drops a few inches when Daisy Geyser erupts and falls lower during a Splendid eruption, so the pool can look half empty. Stay on the boardwalk and keep back from the edge, as the water is near boiling.

The color of the pool shifts throughout the day as sunlight hits the water from different angles and passes through the mineral and bacteria-rich waters. These color changes occur regularly, making the spring feel completely different depending on the time of day you visit.