Firehole River, as seen from entrance to Biscuit Basin boardwalk.

Colorful runoff channels of Sapphire Pool (in distance). This and other colorful runoff channels in Yellowstone are created by a combination of algal thermophiles (microorganisms that thrive in the warm water environments), cyanobacteria, and/or minerals.

Sapphire Pool.The magnificent color comes from the water which reflects blue wavelengths of sunlight combined with the yellow of the sulfur-coated pool.

Mustard Spring




MIDWAY GEYSER BASIN:

The immense Excelsior Geyser leaks nearly 5.8 million gallons (22 million liters) of boiling water a day into the Firehole River below. The geyser has been dormant since 1891, except for a 47-hour-long violent and continuous erunption in September 1985. The crater of Excelsior Geyser measures 200 x 300 feet (60 x 90 meters).

Boardwalk in Midway Basin, approaching Grand Prismatic Spring.

Grand Prismatic Spring - unbelievable! The shear size and variety of colors of this thermal feature makes for an unworldly experience. Grand Prismatic Spring measures more than 370 x 120 feet (111 x 36 meters). The color of this photograph has not been enhanced - this is the way it actually appears.

Opal Pool, as seen along boardwalk after departing Grand Prismatic Spring.

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