Rock  |  Water  |  Wood
Water is an essential element of Yosemite’s landscape.  Many thousands of years ago glaciers carved through the area creating the dramatic vistas.  Nowadays, winter snow and, on many afternoons, summer thunderstorms help fill and replenish lakes, ponds and puddles, feed quiet mountain streams and flowing rivers, and produce slender trickles and dramatic waterfalls.  And of course the water sustains the Parks varied plant and animal life.  The animals include everything from pesky mosquitoes, which find many places to breed in ponds and puddles, to fish and frogs, which make their home in and around the water, to those stopping by for a drink.  While thirsty hikers may well be tempted to drink directly from cool mountain streams alongside trails, the possible presence of Giardia, a protozoan parasite which affects the digestive system, means that it is prudent to filter or purify the water.  Finally, after a long, hot hike, it’s great to cool off in the river, although not directly above a waterfall.
Saddlebag Lake in Inyo National Forest just east of Yosemite National Park.
Tenaya Lake.

Dog Lake (near Lembert Dome; trail from Tuolumne Meadows).

A pond near the Tioga Road entrance.

Puddles on a trail in Tuolumne Meadows.

Soda Springs, a naturally occuring spring in Tuolumne Meadows.

A creek on the trail back to Lembert Dome.

Saddlebag Creek, Inyo National Forest.

The Merced River.

Bridalveil Falls.
Yosemite Falls.

Hydrology - Yosemite National Park

Robert L. Rockwell, PhD..  "Giardia Lamblia and Giardiasis With Particular Attention to the Sierra Nevada," updated March 19, 2002.