One of the most striking things about Yosemite is the juxtaposition of dryness and wetness. The Merced River cascades over granite into the dusty valley and down into the western Sierras. Along the back side of Half Dome the river pools before pouring over Nevada falls. This pool, named Emerald Pool, is a relaxing treelined oasis. The rock wall opposite the John Muir Trail coupled with the water is a great acoustic reflection situation. it's not all gemstones and music for the Merced, however. The drought in California in 2014 has taken a toll on the aquatic health of the river. In addition to running low, the water temperature has risen and algal formations have begun to dominate sections of the river.