This is a timely question, since the Lake Mead National Recreation Area is celebrating its 50th anniversary this year and so, coincidentally, is Viva Las Vegas (Elvis would have turned 79 in January if he was still alive. Yikes!)
Anyhow, here's the story. Lake Mead was created when the Hoover Dam was completed, back in 1936, causing the Colorado River to back up into the canyon behind it. The "bathtub ring" visible around the edge of the lake is caused by a layer of minerals left on the canyon walls when the water level recedes. There have always been lake-level fluctuations depending, logically, on how much water flows in and how much is taken out. According to the Southern Nevada Water Authority, it's currently 1093 feet above sea level, which is low, hence the deep bathtub ring.
However, back in 1964 this level was even lower, down to 1088 feet (per SNWA). This predates decreases in the Rocky Mountain snowpack, the explosive southwest population growth and the attendant increased usage of Lake Mead reserves, and other factors that are currently putting pressure on our water supply. So what other factor was affecting the level back in the mid-'60s?
The answer is Lake Powell.
To back up for a moment (no pun intended), Lake Mead was created west of the Grand Canyon, with water flowing through the canyon first collecting in the lake, before eventually flowing out through the sluices of the Hoover Dam (if it's not tapped for use). Upon exiting, that water empties back into the Colorado River, which flows along the borders of Nevada, Arizona, and California, and through Mexico, before emptying into the Gulf of California.
Lake Powell is situated east of the Grand Canyon, some 180 miles upstream on the Arizona/Utah border, and was created by the Glen Canyon Dam as a storage facility for the Upper Basin states of the Colorado River Compact (Colorado, Utah, Wyoming, and New Mexico), which are obliged to maintain a minimum annual flow of 7,500,000 acre-feet. According to the Wikipedia entry, the last bucket of concrete on the project was poured on September 13, 1963.
Following the creation of the Glen Canyon Dam, much of the water that would previously have gone to Lake Mead was held back to create Lake Powell, which all happened around the same time they would have been filming Elvis and Ann-Margret on those water skis (the 1964 creation of the Lake Mead Recreation Area -- the nation's first -- may well have influenced the decision to depict fun activities on the water in order to promote the new attraction).
Whether the ongoing drought conditions we've been experiencing in recent years are the new normal, or whether we are in the dry phase of a cyclical weather pattern, the answer to your question as to whether the current drought has been ongoing since Elvis went water skiing remains a resounding "no." In fact, according to a recent article on the subject that we came across in the New York Times, the current 14-year drought conditions we're experiencing are almost without precedent across the past 1,250 years: "The once broad and blue river has in many places dwindled to a murky brown trickle. Reservoirs have shrunk to less than half their capacities, the canyon walls around them ringed with white mineral deposits [the "bathtub effect"] where water once lapped. Seeking to stretch their allotments of the river, regional water agencies are recycling sewage effluent, offering rebates to tear up grass lawns and subsidizing less thirsty appliances from dishwashers to shower heads."
What is more, as far as that bathtub ring goes, it's going to get worse before it gets any better because, in the face of the current water-shortage crisis, federal authorities this year will for the first time decrease the amount of water that flows into Lake Mead, the nation’s largest reservoir, from Lake Powell. This will reduce the level of Lake Mead even further, necessitating the massive successive tunnel-digging projects that remain ongoing as it becomes more and more of a challenge to extract water from the diminishing supply in the lake. As things stand, and bearing in mind projections with regard to supply and demand, the specter of future water rationing is becoming increasingly likely: If the level of Lake Mead hits 1,075 feet, the first wave of rationing kicks in; at 1,000 feet the second Las Vegas intake runs dry; and if the level of Lake Powell drops by 100 feet, it will shut down generators that supply electricity to power 350,000 homes.
