The law of unintended consequences

Wired magazine on the world's biggest desalination plant, built to treat more than 35 billion gallons of cruddy, high-saline agricultural runoff per year. But the first step was to placate the Mexican farmers, whose crops were being poisoned by Colorado River water contaminated with runoff from Arizona farms. The fix: Keep the offending runoff out of the river, diverting it from the US side through a 53-mile canal into the Mexican desert. This took care of Mexico's complaints and ended up giving the country a free nature preserve - a wetland habitat now championed by environmental activists.