The water in Yellowstone looks pristine and clear, but don't be fooled to think that it is clean and safe to drink on it's own. Because of the park's immense wildlife populations, there are animals constantly drinking, defecating and dying in and around these waters.
There are long lines (1-3 hours) on weekend mornings, and parking in the valley will fill up and be detoured sometime between 8-10am. These issues are much less during the week.
To protect yourself from disease, treat any river or lake water before drinking. The most reliable way to disinfect water is to boil it for three minutes. Other options include: Use a filter rated to remove bacteria and protozoa (1 micron or smaller filter).
Even if you don't plan on hiking across any streams or rivers, waterproof hiking shoes are a great comfort in Yosemite. As we have mentioned, springtime signals the melting of snow and this causes many trails in Yosemite to have patches of water and ice.
Precipitation falls on Yosemite as rain or snow, some of which immediately runs into lakes and rivers, flowing over Yosemite's spectacular and through magnificent river canyons. Some is stored in snowpack or groundwater, used by plants and trees, or evaporates back into the atmosphere only to fall elsewhere.
Each year, park rangers and search and rescue personnel respond to approximately 250 emergency incidents in the park. Here are some quick tips to help you be safe while hiking in Yosemite: Carry a headlamp on every hike, even short day hikes. Carry and drink plenty of water (a minimum of 1 quart every 2 hours)
Besides the outdoor pools available to the public during summer at Curry Village and Yosemite Valley Lodge, swimming is generally permitted in all bodies of water in the park.
Showers are available at the Curry Village pool showerhouse for a fee. Showers are not available elsewhere in the park. Dump stations are available at Upper Pines Campground (all year), near Wawona Campground (summer only), and near Tuolumne Meadows Campground (summer only).
Picnicking and HikingAlways keep your food within arm's reach and don't turn your back to your food; never leave food unattended. Bears may investigate picnic areas or backpacks for food even in your presence, so be alert.