Sometimes you can smell the Salton Sea all the way to L.A., more than 100 miles from its home in the Imperial Valley desert. The rotten-egg stench is testament to the lake’s birthright as the largest mistake in the history of water. In 1905, the Colorado River blew through a diversion dam used for irrigation and flowed into the Salton Sink salt flat, submerging 400 square miles before the breach was plugged. The water would have evaporated away were it not for runoff from nearby farms. Instead it became a stop for migratory birds and a fleeting tourist draw (hundreds of thousands visited each year). But with nowhere to drain, the water has grown toxic. Each year algal blooms cause enormous fish die-offs and, as the algae decays, that odor. Now that San Diego is buying Imperial Valley farm water, the sea could shrink by half in 20 years, exposing mudflats laced with heavy metals, salt, and agricultural chemicals to the winds. Re-adding freshwater could cost $4 billion to $10 billion. But for a fraction of that, we could cap dusty areas with gravel or clay and restore natural wetlands for birds in the Colorado’s delta, nearby in Mexico.