Lake Mead's Bathtub Ring

The white band on the canyon walls above the water is not paint. It is calcite, deposited over decades when the lake sat higher, a tide line left by the Colorado River's retreat.

Lake Mead is the largest reservoir by volume in the United States, created by Hoover Dam in the nineteen thirties when the Colorado River was impounded behind four million cubic yards of concrete. Its water was allocated under the nineteen twenty-two Colorado River Compact, an agreement between seven western states that divided the river's flow based on measurements taken during an unusually wet period. The river, it turned out, does not carry as much water as the compact assumed. The states have been drawing on a promise the river cannot consistently keep.

Between two thousand and two thousand twenty-three, the lake's surface dropped more than one hundred forty feet, exposing the white calcite band in ever-wider contrast against the red canyon rock. At the low points, objects that had been underwater since the reservoir filled began to surface: a boat that had sunk decades earlier, human remains found in a barrel in two thousand twenty-two whose identity and circumstances remained under investigation.

Las Vegas gets roughly ninety percent of its water from Lake Mead. The city has invested heavily in water recycling and conservation, reducing per-capita consumption even as the metropolitan population grew. The mathematics of the Colorado River system, however, are not resolved by efficiency alone. The states that depend on the river, from Wyoming to Mexico, are negotiating an allocation they have not agreed on since nineteen twenty-two.

The ring on the walls is a measuring instrument. It tells you where the water was and where it is not.