Because of its tremendous ecological effect on the Colorado River, the Glen Canyon Dam has been subject to decades of criticism from the environmental movement. Being located in a high desert climate amid porous geology, Lake Powell causes huge evaporation and seepage losses. The Glen Canyon Institute estimates that is lost from the reservoir in an average year. This amounts to 6 percent of the Colorado River's flow, an increasingly valuable amount of water in an arid land for both humans and the animals and plants that live along the river. (This amount greatly decreases when Lake Powell is low; with the reservoir about half full in water year 2015, evaporation was .)