Nearly every coastal region on Earth faces a hidden threat beneath the surface. A new global study has found that saltwater is pushing into underground freshwater supplies along coastlines worldwide, putting drinking water and farmland at risk on every inhabited continent.
The research, published in May 2026, mapped the vulnerability of coastal groundwater aquifers across the planet. The findings show that the problem is not limited to a few hotspots. It is a global phenomenon.
From Vietnam to the U.S. East Coast, the salt line is moving inland
Saltwater intrusion happens when ocean water seeps into freshwater aquifers. This can occur naturally, but human activities and rising seas are accelerating the process. The study identified regions in Southeast Asia, the Middle East, West Africa, and the eastern United States as particularly vulnerable.
In Vietnam, the Mekong Delta has seen saltwater creep deeper into farmland, damaging rice crops. Along the U.S. Atlantic coast, farmers in states like Maryland and Delaware have watched their fields turn too salty to grow corn or soybeans. The study notes that low elevation and heavy groundwater pumping make these areas prone to intrusion.
Local communities care because the consequences are immediate. Wells that once provided clean drinking water become brackish. Crops fail. Livestock cannot drink the water. For coastal towns that rely on groundwater as their primary water source, the shift can force expensive changes, such as building desalination plants or piping in water from farther away.
A quiet crisis that demands attention before taps run dry
The study's authors analyzed data from thousands of monitoring wells and used computer models to project future risks. They found that even under moderate climate scenarios, the area of coastal land threatened by saltwater intrusion could expand significantly by the end of the century.
Groundwater is often out of sight and out of mind. Unlike rivers or lakes, it is not visible when it becomes polluted. But for the roughly 40 percent of the world's population that lives within 100 kilometers of a coast, this invisible shift has very visible effects. The study calls for better monitoring and more careful management of groundwater extraction to slow the advance of saltwater.
The research makes clear that saltwater intrusion is not a distant problem. It is already happening, from the rice paddies of Vietnam to the cornfields of the United States. The question is how fast it will spread and whether communities can adapt before their wells turn salty.
