cbs report ben casey is showing us two decades of drought is threatening a critical western supply. >> reporter: it is hard to believe that a place this beautiful is a shadow of its former self. >> lake powell has been on a decline in the last two decades. >> reporter: glen bellk runs the canyon institute which was once flooded to create lake powell, the nation's second largest reservoir. >> this area right now is 177 feet below full pool. >> reporter: when is the last time it was that high? >> full was 1979. >> reporter: that full bathtub ring is where it used to be, and that is the result of the mega drought, and the lake is now 24% full. >> it looks like we can expect this to be new normal. >> reporter: climate change is making the west hotter and drier and threatening the colorado river system, and threatening lake powell in colorado and utah and lake mead and providing water for people in 12 states. >> and you had 12 ramps and this is all you got? >> this is all we have got. >> reporter: and they have closed down 12 boat ramps in 12 areas, and could cause the glenn canyon dam to