The lake that formed when the dam was completed filled Glen Canyon with more than 150 meters (450 feet) of water, stretching approximately 300 kilometers (186 miles) to the northeast from the dam. The water also filled all the side canyons that were below the water level and infiltrated the porous sandstone of the canyon walls. The dam significantly changed the hydrologic cycle in the area by increasing the amount of water flowing into the ground and contributing massive amounts of water to the atmosphere through evaporation from the lake's surface.

The geosphere also changed significantly in response to the dam. The free-flowing river had carried thousands of tons of sediments downstream each year. With the water held back by the dam, the sediments it carried also began accumulating behind the dam, filling in the space meant for water storage.