Scientists have found a gigantic freshwater aquifer hidden deep below the ocean. The surprising discovery, from a new survey of the sub-seafloor off the northeast U.S. coast by researchers from Columbia University, appears to to be the largest formation of this type anywhere in the world — stretching from Massachusetts to New Jersey and extending continuously out about 50 miles to the edge of the continental shelf. Researchers said that if it was discovered on the surface it would create a lake covering some 15,000 square miles.