In 1996, the phrase “Gulf of Mexico hypoxia” became common for agricultural scientists, regulatory agencies, the fertilizer industry, and even some farmers because the accusation was made that inefficient use of nitrogen fertilizer in the Mississippi River Basin—and especially the Upper Midwest—was creating a “dead zone” in the Gulf. There is no question that this oxygen-depleted (< 2 ppm) area exists, and that since 1993, it has remained larger than the long-term historical size (Fig. 1).