This is Glen Canyon National Recreational Area. Normally this cavern is filled with water. It's not because of drought. This is an article in the New York Times.

http://www.nytimes.com/2005/04/08/travel/escapes/08canyon.html?8hpib

The problem with this project is that it was mismanaged from start. The Powell Dam is constructed with walls of Navajo Sandstone. It is very porous and the areas within the sandstone like this cavern were of limestone and/or shale. Those type of rocks erode very quickly. The sandstone filled with water in it's banks before it fills the Powell Dam Reservoir. The water retained in the 'banks' and caverns are mostly unavailable for consumer use and ENHANCES the drought.