The Delaware River Basin Commission directed emergency reservoir releases beginning in October 2024, dumping about 1.12 billion gallons of water by early November to push back a wall of salt creeping upriver toward drinking-water intakes that serve millions of people. The effort highlights a growing threat along coastlines across the United States: saltwater is migrating into the rivers and aquifers that supply tap water, driven by drought, rising seas, and heavy groundwater pumping. For communities from southern New Jersey to Long Island to Florida, the question is no longer whether salt will reach their water, but when.
How Salt Moves Into Freshwater Supplies
Saltwater intrusion works through two distinct pathways, and both are accelerating. In rivers and estuaries, the boundary between fresh and salt water, known as the salt front, shifts upstream when drought reduces river flow or when tides push harder against weakened currents. The Delaware River regulators track this boundary as the point where chloride concentration reaches 250 milligrams per liter, the federal drinking-water quality standard, and report it as a seven-day average location. When the salt front migrates past a water intake, utilities must either shut down the intake or blend contaminated water with cleaner reserves, a choice that can strain already-limited supplies during dry periods.
Underground, the mechanics differ but the outcome is the same. The U.S. Geological Survey identifies lateral encroachment and vertical upconing as the two main physical mechanisms. Lateral encroachment happens when seawater pushes inland through aquifer layers as freshwater levels drop. Upconing occurs when a pumping well draws saltwater upward from deeper saline zones. Both are worsened by heavy groundwater extraction and sea-level rise, and both can render wells permanently unusable. The Environmental Protection Agency frames the risk around three converging pressures: sea-level rise, drought, and growing water demand, each of which magnifies the others and leaves coastal communities with shrinking safety margins.
Wells Already Lost From New Jersey to Long Island
The damage is not hypothetical. A USGS investigation in Cape May County documented the abandonment of at least 10 public-supply wells and more than 100 domestic wells between 1960 and 1990 because of rising chloride levels. That report also tracked chloride trends in individual wells over time, showing a steady inland advance as pumping lowered freshwater heads and allowed denser seawater to move landward. Local utilities were forced to drill new wells farther inland and deeper into the aquifer system, a costly adaptation that bought time but did not eliminate the underlying pressure driving intrusion.
Since then, the problem has spread beyond a handful of New Jersey shore towns. Hundreds of wells across southern New Jersey have been shut down as salt contamination worsened, cutting off long-standing sources of drinking water and irrigation. On Long Island, where nearly all drinking water comes from groundwater, utilities have reported increasing concern about chloride levels near the coasts and in low-lying neighborhoods. Saltwater was detected in Long Island aquifers in 2020, according to national reporting on coastal risks, underscoring that even heavily monitored systems can be caught off guard when drought and sea-level rise align.
Evidence of a Widespread Structural Vulnerability
On Long Island specifically, population growth and climate change are compounding the stress on groundwater, but the emerging science indicates that the vulnerability is national in scope. A peer-reviewed study in Nature Communications analyzed roughly 250,000 coastal groundwater-level observations collected since 2000 and found that significant fractions of the U.S. coastline are characterized by landward hydraulic gradients. In practical terms, that means the pressure conditions that allow seawater to flow toward freshwater wells already exist in many places, even where no obvious contamination has yet been detected.
That finding challenges the common assumption that intrusion is limited to a few well-known hotspots, such as South Florida or parts of the Chesapeake Bay. Instead, it suggests a structural vulnerability running along much of the American coast, driven by a combination of low-lying topography, intensive groundwater development, and rising seas. For utilities and regulators, the implication is that waiting for chloride spikes to appear in monitoring wells may be too late. Proactive measures, such as reducing pumping near shorelines, relocating well fields inland, or developing alternative supplies, will likely be needed in many regions long before residents taste salt in their tap water.
Emergency Releases and the Limits of Flow Management
The DRBC’s approach on the Delaware River represents one of the most active defenses against surface-water intrusion in the country. The commission manages upstream reservoir releases specifically to maintain enough flow at Trenton, New Jersey, to keep the salt front downstream of drinking-water intakes that serve Philadelphia and nearby suburbs. When drought conditions tightened in the fall of 2024, the DRBC directed releases that totaled about 1.12 billion gallons as of early November, and called a special public hearing on drought operations for the basin to weigh how much more stored water could be safely deployed.
But this strategy has a built-in tension. Every gallon released from upstream reservoirs to fight salt on the estuary is a gallon unavailable for other uses, including municipal supply for New York City and agricultural needs in the upper basin. During prolonged drought, the reservoirs themselves draw down, narrowing the margin for future emergencies and raising the possibility of competing shortfalls: not enough flow to hold back the salt front, and not enough storage to meet inland demands. Meanwhile, the approach does nothing for groundwater intrusion, which operates on a slower but less reversible timeline. Once salt contaminates an aquifer, flushing it out can take decades or may never fully succeed, especially in confined systems where natural recharge is limited and where the density contrast between fresh and saline water maintains a persistent interface.
Salt Damages Infrastructure Before It Reaches the Tap
Most public discussion focuses on whether salt makes water undrinkable, but a less visible problem may hit communities first. A synthesis published in the Annual Review of Marine Science found that sea-level-rise-driven groundwater changes can corrode buried pipes, degrade building foundations, and compromise subsurface utilities even before coastal flooding occurs. Salt can become a driver of infrastructure failure as it saturates shallow soils and groundwater, rusting rebar in concrete, weakening roadbeds, and shortening the lifespan of stormwater and sewer networks. These impacts often emerge in low-lying neighborhoods where groundwater is already close to the surface, creating chronic maintenance burdens long before residents notice any change in the taste of their water.
Because these processes unfold underground, they can be easy to overlook in planning documents that focus on surface flooding and storm surge. Yet the same rising seas that push salt into rivers and wells also raise the water table, shrinking the unsaturated zone that protects building foundations and utility corridors. As chloride-rich groundwater interacts with metals and concrete, corrosion accelerates, leading to more frequent leaks, sinkholes, and structural damage. For cash-strapped coastal municipalities, the hidden costs of saltwater intrusion may show up first as escalating repair bills and service disruptions, even if drinking-water quality remains within regulatory limits for years.
Planning for a Salty Future
Managing this emerging threat will require better data as well as new policies. Detailed hydrogeologic mapping, chloride monitoring, and modeling can help utilities identify which well fields and intakes are most at risk under different sea-level and drought scenarios. Many of the technical tools needed are already available through federal agencies. For example, communities can draw on USGS mapping resources to understand local aquifer geometry, surface elevations, and historical water levels. Combined with targeted field studies, such information can guide decisions about relocating wells, redesigning distribution systems, or investing in desalination and advanced treatment where no other options exist.
At the same time, experts stress that adaptation must go beyond engineering fixes. Reducing groundwater demand through conservation, leak detection, and water reuse can slow the inland march of salt and extend the life of vulnerable aquifers. Land-use planning that steers new development away from the lowest-lying areas can limit future infrastructure exposure to corrosive groundwater. And in basins like the Delaware, where surface flows are actively managed, drought plans may need to account explicitly for salt front dynamics, not just total water availability. The experience of Cape May, Long Island, and other early hotspots suggests that communities that act before salt shows up in their taps will have more options (and lower costs) than those forced into emergency responses once the intrusion is already underway.
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*This article was researched with the help of AI, with human editors creating the final content.
