Who would have believed it? Water levels at Lake Powell have dropped to 50 percent for the first time since it filled in 1980. This draining is likely to continue to the point where the reservoir could vanish in the next three-to-four years.

With snowpacks below 25 percent of normal, and continued warnings from the U.S. Geological Survey, EPA and others that a severe and sustained drought should be anticipated, Lake Powell's days may be numbered. A 1995 study published by the American Water Resources Association predicted that a severe drought would lead to Lake Powell's draining within eight years. Things are right on schedule.

Now that Lake Powell is down by some 87 feet, three boat ramps have been closed: Antelope Point, Stateline and Hite. The National Park Service is working with a $3 million emergency appropriation to extend other ramps as the reservoir continues to decline. But construction of the recently approved $70 million Antelope Point marina complex is in limbo, because boats can’t be launched from what has been revealed by drought to be a cliff.

Once Lake Powell drops an additional 28 percent, it will no longer generate hydroelectricity because Glen Canyon Dam's penstocks will be exposed, and water will no longer be able to turn the generators. There's also a problem with sediment, since fluctuating river flows that occur during low reservoir levels will speed the movement of sediment toward Glen Canyon Dam.

The U.S. Geological Survey says that major droughts of the past, such as the years from1942 to 1977, went largely unnoticed. We notice this drought because the West has four times the population and we’ve been mining our groundwater.

Federal scientists have also informed us that the previous century was 20 percent wetter than normal. That means our ability to put water to work was helped by luck as much as it was by massive engineering projects. Even at those inflated levels, Colorado River water allocations are 20 percent above what the river delivered.

We’ve managed to avoid crises in the past because not all the Colorado River Basin states used their full allocations. Even so, the river reached the sea only twice in the past two decades. Add to all this a drought cycle that is predicted to last 25 years, and Lake Powell, along with every other reservoir in the upper Colorado River storage system, won’t have water to store.

Vanishing bodies of water in the Western United States shouldn’t surprise us: It's part of our legacy. In 1890, the Geological Survey's first professional paper discussed the principles of global climate change. The publication analyzed how a body of water that was once 800 feet deep -- Lake Bonneville -- had reduced itself into the briny and shallow Great Salt Lake.

In the 19th century, the physical geography of the planet provided undeniable evidence that humans can become victims of climate change. In the 20th century, we gained new tools, such as tree-ring data, that allowed us to reconstruct the climate of the last 400 years. This reaffirmed that the Earth’s climate varies dramatically. Whether these changes result from the effects of greenhouse gases or from natural cycles, the results are the same.

Scientists have given us ample warning, but our water-management experts don't listen. At a recent gathering in Moab, Utah, John Keys, Commissioner of the Bureau of Reclamation, worked to calm the fears of those concerned that the Colorado River may soon be unable to provide for the 25 million people plumbed into his system.

"They (the reservoirs) are doing exactly what they were designed to do," he said. But when it was pointed out that these reservoirs are declining over 10 percent per year, and thus could empty in another five to six years, he had no plan for how the federal government would handle the shortages.

Certainly many of us will be pleased to see the uncovering of Glen Canyon. It will be nature’s way of reminding us that we are not in control.

It would be truly unfortunate, however, if the warnings these declining levels represent are not heeded, and all those presently reliant on the overuse of Colorado River water get plunged into a crisis with no plan of action.

John Weisheit is a contributor to Writers on the Range, a service of High Country News in Paonia, Colorado (hcn.org). He is conservation director of the nonprofit group, Living Rivers, in Moab, Utah.