All thermal waters contain organisms that may cause illness, including skin rash, gastrointestinal illness (vomiting and diarrhea), or other infections that can be life-threatening. The risk of contracting these infections in Yellowstone is not known to be higher than any other natural body of thermal water. To minimize the risk of illness from swimming and soaking in Yellowstone: Avoid submerging your head or activities that cause water to enter your nose. If you submerge your head, wear nose plugs or hold your nose shut.