This morning the Colorado River was let loose to "flood" the Grand Canyon, as it did years ago before the Glen Canyon Dam was built and Lake Powell filled. The Bureau of Reclamation released Monday a final environmental assessment (FEA) and a Finding of No Significant Impact (FONSI) that authorized the initiation today's high-flow test which will last three days.

This gives you a glimpse of what nature has been doing for millions of years, cutting through and creating this magnificent canyon," Secretary of the Interior Dirk Kempthorne told AP after he let Colorado loose.

The flood is being carried out because more sand is needed to rebuild sandbars throughout the 277-mile reach of Grand Canyon National Park. It is being supervised by scientists and resource managers from Interior’s U.S. Geological Survey (USGS), Reclamation, National Park Service, U.S. Fish and Wildlife Service, and Bureau of Indian Affairs.

A stunning maximum amount of approximately 41,500 cubic feet (300,000 gallons) per second will flow for about 60 hours, enough water to fill the Empire State Building in 20 minutes, Kempthorne said. Sandbars that form downstream from the dam are essential to native plant and fish species.

However, the river is now cool and clear as its sediment is being blocked by the dam, which means that from time to time action has to be taken to prevent the extinction of fish species and other elements of the ecosystem.