Under the undrinkably salty water of the ocean off the northeastern coast of the United States lies a gigantic deposit of relatively fresh water, scientists have found.

The aquifer, a layer of water-bearing porous sediments, generally begins about 600 feet below the ocean floor and bottoms out at about 1,200 feet.

It generally stretches about 50 miles out from shore, and it runs at least from Massachusetts to New Jersey, researchers said in a statement from the Earth Institute at Columbia University.

If it were on the surface, it would be a lake covering about 15,000 square miles, about twice the size of Lake Ontario. And researchers estimate it contains at least 670 cubic miles of water.


“We knew there was fresh water down there in isolated places, but we did not know the extent or geometry,” Chloe Gustafson, a doctoral candidate at Columbia University’s Lamont-Doherty Earth Observatory, said in the statement. Gustafson was the lead author of a study on the aquifer that was published last week in the journal Nature Scientific Reports.

The formation appears to be the largest found so far in the world, the statement said.

Gustafson and her fellow researchers, who included a scientist from the Woods Hole Oceanographic Institution in Massachusetts, raised the prospect that the underground water could be tapped in places “where onshore freshwater resources have diminished.”

“The low-salinity groundwater we have imaged represents a significant resource with potential for future offshore groundwater production,” the study said.

Kerry Key, a study coauthor, said in the statement that it could be a boon if similar aquifers were found in places that are running out of water, like Southern California, Australia, the Mideast, or Saharan Africa. The group is hoping to expand its surveys.

The researchers used an innovative electromagnetic imaging technique to look under the ocean floor, the statement said.


Key and Rob L. Evans of the Woods Hole Oceanographic Institution spent 10 days in 2015 making measurements off southern New Jersey and Martha’s Vineyard that were key to the discovery.

The water may have been trapped there thousands of years ago as oceans rose after the last glacial age, but researchers also believe the aquifer may now be fed by modern underground runoff from the land.

The water is freshest near the shore and saltier farther out. Fresh water on land contains less than 1 part per thousand of salt. That’s the concentration in the aquifer near land.

But the salt content rises to 15 parts per thousand at the outer edges. Seawater is typically 35 parts per thousand.

Water scarcity is among the main problems facing many societies, with an increasing number of regions chronically short of water, the United Nations says. Water stress is expected to grow as demand for water increases and the effects of climate change intensify.

In coastal areas, there is plenty of undrinkable saltwater, and desalination is costly.

Offshore aquifers like the one found off the Northeast “could turn out to be an important resource in other parts of the world,” Gustafson said.

Gustafson said in an e-mail that many steps would have to be taken before offshore freshwater wells could become a reality, including further assessment of the “nature and geometry” of the deposits, scientific drilling, and the building of infrastructure for extraction and transport of the water.


“Before drilling is considered,” she also said, “a proper environmental impact assessment study should take place.”

An electromagnetic receiver being deployed off a research vessel
An electromagnetic receiver being deployed off a research vesselKerry Key

Martin Finucane can be reached at martin.finucane@globe.com.