Why This Year's Gulf Dead Zone Is Twice As Big As Last Year's

First, the good news: The annual "dead zone" that smothers much of the northern Gulf of Mexico—caused by an oxygen-sucking algae bloom mostly fed by Midwestern farm runoff—is smaller this year than scientists had expected. In the wake of heavy spring rains, researchers at the National Oceanic and Atmospheric Administration had been projecting 2013's fish-free region of the Gulf to be at least 7,286 square miles and as large as 8,561 square miles—somewhere between the size of New Jersey on the low end to New Hampshire on the high end. Instead, NOAA announced, it has clocked in at 5,840 square miles—a bit bigger than Connecticut. It's depicted in the above graphic.

Now, for the bad news: This year's "biological desert" (NOAA's phrase) is much bigger than last year's, below, which was relatively tiny because Midwestern droughts limited the amount of runoff that made it into the Gulf. At about 2,900 square miles, the 2012 edition measured up to be about a third as large as Delaware.