Yosemite and Tioga Pass Area

Glacial lakes are formed when a glacier erodes the land, and then melts, filling the hole that it has created. The scouring action of the glaciers pulverizes minerals in the rock over which the glacier passes. These pulverized minerals become sediment at the bottom of the lake, and some of the rock flour becomes suspended in the water column. These suspended minerals support a large population of algae, making the water appear green.