"With temperatures that average temperate of 191.1°F (88.4°C), Crested Pool is almost constantly boiling, sometimes to 6 feet (2 m) or more. The extreme heat prevents most bacterial growth, resulting in exceptionally clear blue water. Boiling is particularly active along the intricate sinter formation circling the spring, the “crested” edge. Listen for the sizzling. Crested Pool has an average pH of 8.9 and an average conductivity of 2269 uS/cm." 

Look closely at the lower right portion of the image and you'll see both bison hoof prints and human foot prints. There are signs around the park warning of the dangers of leaving the boardwalk. The crust near hot springs, geysers, fumeroles and mud pots is very thin and the environment around thermal areas is fragile. While bison can't read signs, humans can and should heed the warnings for their own safety as well as the park's preservation.