The drought isn't just stranding boats on the Mississippi, it's turning the river salty. The low outflow is allowing saltwater from the Gulf of Mexico to creep upstream at a rate of around a mile day, NPR reports. Some Louisiana cities have already been forced to buy water from elsewhere and New Orleans is now at risk. "We've been through four hurricanes and an oil spill and if you'd have told me this was going to happen, I wouldn't have believed you," says the president of Plaquemines Parish, south of New Orleans.
"Saltwater hugs the bottom of the river because it's heavier, denser than the freshwater. And that's what makes it a wedge, not a wall," explains the director of the Tulane Institute on Water Resources. "And right now, given the low flows in the Mississippi and the level of the Gulf, we're watching the water make its way toward New Orleans." The US Army Corps of Engineers is building an underwater dam to stop the saltwater, as it did in 1988 and 1999. Officials in New Orleans say they don't expect the city's drinking water to start tasting salty, and only people on low-sodium diets should worry about health risks. (Read more Mississippi River stories.)