A massive freshwater reservoir was discovered beneath the Atlantic Ocean — stretching from Massachusetts to New Jersey, according to researchers.

The rare find was reported by experts at Columbia University last week following a multi-year, sub-seafloor study.

“We knew there was fresh water down there in isolated places, but we did not know the extent or geometry,” explained lead researcher Chloe Gustafson, a Ph.D. candidate at Columbia’s Lamont-Doherty Earth Observatory.

“It could turn out to be an important resource in other parts of the world,” she said in a statement.

Using electromagnetic waves, Gustafson’s team was able to map the underwater “aquifer” — which stretches out about 50 miles to the edge of the continental shelf.

“If found on the surface, it would create a lake covering some 15,000 square miles,” her team wrote in its report. “The study suggests that such aquifers probably lie off many other coasts worldwide, and could provide desperately needed water for arid areas that are now in danger of running out.”

According to researchers, the first signs of the Northeast underwater reservoir came in the 1970s when companies were drilling for oil. The workers would sometimes hit fresh water, thus causing many to believe that something was down there.

“Analyses indicated that the deposits are not scattered; they are more or less continuous, starting at the shoreline and extending far out within the shallow continental shelf — in some cases, as far as 75 miles,” the researchers said. “For the most part, they begin at around 600 feet below the ocean floor, and bottom out at about 1,200 feet.”

Gustafson’s team, which published their findings in the journal Scientific Reports, believes the reservoir’s water “probably got under the seabed in one of two different ways.”

“Some 15,000 to 20,000 years ago, toward the end of the last glacial age, much of the world’s water was locked up in mile-deep ice; in North America, it extended through what is now northern New Jersey, Long Island and the New England coast,” the researchers explained.

“Sea levels were much lower, exposing much of what is now the underwater US continental shelf. When the ice melted, sediments formed huge river deltas on top of the shelf, and fresh water got trapped there in scattered pockets. Later, sea levels rose.”

In order to one day use the water for consumption, scientists would have to desalinate it.

“We probably don’t need to do that in this region,” said study co-author and geophysicist Kerry Key. “But if we can show there are large aquifers in other regions, that might potentially represent a resource.”