A Massive 20,000-Year-Old Freshwater Reservoir Found Off the East Coast Could Power New York City for 800 Years
A newly confirmed subsea water reservoir beneath the U.S. Atlantic continental shelf is challenging long-held assumptions about the distribution of Earth’s groundwater resources. Located off the northeastern seaboard, the formation had remained largely undetected for decades despite its proximity to major urban centers and coastlines.
In 2025, an international team of geoscientists recovered deep-sea core samples from the region. These confirmed the presence of a low-salinity underwater aquifer, buried hundreds of meters beneath the ocean floor and sealed under dense marine sediment. Though not currently exploited, the reservoir is one of the largest offshore groundwater systems identified in North America to date.
The find comes amid mounting concern over freshwater scarcity, particularly in coastal zones vulnerable to sea-level rise and saltwater intrusion. Hydrologists and policy analysts are now evaluating whether such fossil freshwater bodies might serve as emergency reserves or simply as geological archives of past climate conditions.
Deep-Sea Drilling Reveals Ice Age Water Beneath Atlantic Seafloor
Between May and August 2025, scientists aboard the L/B Robert conducted three test borings off the coast of Massachusetts, targeting locations near Martha’s Vineyard and Nantucket. The operation, part of IODP³-NSF Expedition 501, retrieved more than 13,000 gallons of water from as deep as 400 meters below the seabed. Expedition leaders included Brandon Dugan of the Colorado School of Mines and Rebecca Robinson of the University of Rhode Island.
To extract water samples, researchers drilled into the seafloor at three locations off Martha’s Vineyard and Nantucket. Credit: Rainer Lesniewski/Getty Images
Salinity levels in the reservoir varied by distance from the shore. The site closest to Nantucket registered 1 part per 1,000, within safe drinking limits. At the outermost site, salinity reached 17 to 18 parts per 1,000, roughly half that of typical seawater. All samples were collected from below a thick clay and silt layer that effectively isolated the freshwater zone from the surrounding marine environment.
Initial isotopic and geochemical data indicate the reservoir has remained intact since the last glacial maximum, roughly 20,000 years ago. The samples are currently under post-expedition analysis at the Bremen Core Repository in Germany. ECORD, which manages the project, confirmed that final interpretation will include microbial, pore-space, and rare earth element analysis to improve modeling of the aquifer’s volume and structure.
Reservoir Formed by Glacial Melt During Ice Age
The reservoir’s formation is linked to glacial meltwater that once flowed across the then-exposed continental shelf when sea levels were lower. As thick ice sheets advanced and retreated, pressure from the ice forced meltwater into porous sediment layers. Over time, rising seas buried these layers beneath marine deposits, trapping the freshwater in place.
Geochemical analysis suggests the reservoir originated from glacial meltwater forced into sediment during the last glacial maximum, later trapped under rising sea levels and impermeable marine deposits. Credit: Shutterstock
This mechanism aligns with earlier modeling by Dugan and Mark Person, who first proposed plausible emplacement scenarios in a 2003 study. Their findings, later published in the Geological Society of America Bulletin, identified glacial injection as a dominant driver of offshore freshwater accumulation in formerly glaciated margins.
Dugan confirmed the team ruled out topography-based recharge, noting that the New England coastline lacks significant elevation. He stated: “There might be a rainfall component blended in the glacier water… it’s probably a mixed system.”
The concept of offshore freshened groundwater (OFG) has gained momentum in recent years. Although smaller aquifers have been documented off Australia, Southeast Asia, and southern Africa, few offer the same level of preservation and accessibility seen along the northeastern U.S. margin. Expedition 501 marks one of the first physical confirmations of a large OFG system in this region.
Legal, Technical, and Environmental Hurdles Remain
Despite its potential as a strategic freshwater reserve, the reservoir is not being developed for human use. Significant legal, environmental, and engineering questions must be addressed before extraction could be considered. The system lies within the U.S. Exclusive Economic Zone, yet no federal guidelines currently exist for accessing or managing subsea aquifers.
Though rich in freshwater, the subsea reservoir faces significant barriers to use, including unclear legal frameworks, engineering limitations, and ecological risks tied to deepwater extraction. Credit: GeologyIn
Conventional groundwater pumping methods cannot be applied in marine settings without risk. Extraction could compromise sediment integrity, increase saltwater mixing, or disturb surrounding ecosystems. Scientists from the Colorado School of Mines are now refining geophysical models to assess these risks under different pressure and volume scenarios. Dugan’s project site provides more detail on the technical aspects of this ongoing research: dugan-brandon project overview.
Accurately estimating the reservoir’s capacity remains difficult. Variables such as porosity, sediment composition, and hydraulic conductivity are still being evaluated. Expedition members are also studying rare earth signatures and microbial data to trace the water’s age and origin more precisely. The research will guide future efforts to identify similar systems on other continental shelves.
Discovery Opens Global Search for Subsea Freshwater
The 2025 discovery has energized international interest in paleoclimate archives preserved under the seafloor. As nations confront worsening droughts and overexploited aquifers, some have begun surveying offshore regions once thought to be hydrogeologically irrelevant. Electromagnetic imaging and borehole logging are being used to map suspected OFG bodies worldwide.
Much of the current work builds on anomalies first observed by the U.S. Geological Survey during mid-20th century offshore surveys. Those early findings were largely forgotten until Dugan and Person reanalyzed the data in the early 2000s. Their models helped frame the search that led to the confirmed reservoir discovery, as reported by Live Science.
The National Science Foundation is now reviewing proposals for additional offshore drilling campaigns along the Mid-Atlantic and South Atlantic margins. Whether these reservoirs are ultimately preserved, tapped, or classified as critical infrastructure remains uncertain.
