Yellowstone has some hazards related to volcanic activity. There are also hazards from dangerous animals.
Though many of the animals in the park are used to seeing humans, the wildlife is nonetheless wild and should not be fed or disturbed. According to park authorities, stay at least 100 yards/meters away from bears and wolves and 25 yards/meters from all other wild animals! No matter how docile they may look, bison, elk, moose, bears, and nearly all large animals can attack. Each year, dozens of visitors are injured because they didn’t keep a proper distance. These animals are large, wild, and potentially dangerous, so give them their space.
In addition, be aware that odors attract bears and other wildlife, so avoid carrying or cooking odorous foods and keep a clean camp; do not cook or store food in your tent. All food, garbage, or other odorous items used for preparing or cooking food must be secured from bears. Treat all odorous products such as soap, deodorant, or other toiletries in the same manner as food. Do not leave packs containing food unattended, even for a few minutes. Animals which obtain human food often become aggressive and dependent on human foods, and many can suffer ill health or death from eating a non-native diet. A short film about food safety is now mandatory before a back country permit will be issued.
Fragile sinter crusts and ledges can give way, plunging a careless tourist into the boiling waters below
Always stay on boardwalks in thermal areas. Scalding water lies under thin, breakable crusts; pools are near or above boiling temperatures. Every year visitors traveling off trail are seriously burned, and people have died from the scalding water. Park rangers can also issue $130 fines for being out of bounds, or much more if there is any geological damage. It’s common to get sprayed with fine mist from the geysers, though. You don’t need to worry about being burned, as the water has traveled sufficient distance to cool down, provided you’re within the designated areas. However, glass lenses (such as eyeglasses and camera lenses) may be permanently damaged by the high mineral content of the water in the mist. For cameras, clear glass filters can provide inexpensive protection for high-priced lenses (be sure to have some replacements). If water from a thermal feature gets on a vulnerable lens, it must be washed off immediately (if no clean water is available, you can try – no, this is not a joke – licking the lens); if you try to wipe off the geyser water with a cleaning cloth (without rinsing the lens first), you risk grinding the suspended minerals into the glass of the lens and scratching it.
It is illegal to swim or bathe in thermal pools. There is a designated swimming area along the Firehole River near Madison Junction.
This is one of the largest, high-altitude bodies of fresh water on the planet. The Lake is large enough to have its own weather effects, and conditions can change rapidly. More than a few fatalities have occurred on the lake, when boaters fell victim to weather conditions that went from calm and sunny to violent storm in a matter of minutes. East of West Thumb Geyser Basin, near Lake Village, there is a marina where boats are available for rental from a Park concessionaire.
Know your 10 essentials when going on a hike, cell phones won’t work in most areas of the park, and may not be depended on in an emergency situation. 1. Navigation 2. Hydration & Nutrition 3. Pocket Knife 4. Sun Protection 5. Insulation 6. Ability to make fire 7. Lighting 8. First Aid 9. Shelter 10. Whistle
The weather can change rapidly and with little warning. A sunny, warm day can quickly become a cold, rainy or even snowy experience even in summer. Hypothermia can be a concern. Be prepared for a variety of weather conditions by bringing along appropriate clothing. Lightning can and does injure and kill people in the park, so watch the sky and take shelter in a building if you hear thunder. If you don’t like the weather, wait 10 minutes; it’ll probably change.
When camping, either filter, boil, or otherwise purify drinking water. Assume that even crystal clear waters may be polluted by animal and/or human wastes, and intestinal infections from drinking untreated water are increasingly common. Iodine tablets are not as effective as other methods but are readily available at local stores and easy to bring on a hike.
Finally, with so many people visiting the park each year petty crimes are something to be vigilant against. Lock your car doors and exercise sensible precautions with valuables, especially when leaving cars near trail heads or other areas where you might be away from your car for any length of time.
As a US National Park, Yellowstone is subject to US Federal Law. Generally, permits (such as for fishing) issued by surrounding States are not valid in the Park. If a visitor is cited for an offense while in the Park (such as speeding, feeding wildlife, failing to secure food in a campsite, etc), the fine must be paid immediately. The visitor is then free to make their case to the court at the Park Headquarters in Mammoth Hot Springs.