It’s wild to think that the world’s landmasses are surrounded by ocean water, yet if any of that saltwater intrudes into the landmasses, the consequences are sometimes dire. When this happens, it’s referred to as saltwater intrusion.

Saltwater intrusion is the movement of salt water into freshwater aquifers, which can lead to contamination of drinking water sources and degradation of ecosystems. This phenomenon typically occurs in coastal regions where the balance between freshwater and saltwater is disturbed, which can occur in several different ways.

• Excessive groundwater pumping: As freshwater levels in an aquifer drop, the natural pressure that keeps saltwater at bay decreases, allowing seawater to seep inland and upward into the groundwater system. This poses serious risks to agriculture, drinking water supplies, and natural habitats.
• Hurricanes: When a hurricane pushes a surge of seawater onto the land, that salty water can flood coastal areas and seep into the soil and shallow aquifers. If the storm surge is powerful enough or lasts long enough, the saltwater can infiltrate freshwater wells, wetlands, as well as rivers and lakes. This can lead to temporary contamination of drinking water supplies and damage to crops, especially those not tolerant of high salinity.
• Sea level rise: As ocean levels rise due to climate change, saltwater can more easily seep into freshwater aquifers, rivers, and wetlands. Under normal conditions, freshwater stored underground in coastal aquifers creates pressure that helps keep seawater at bay. But as sea levels rise, this delicate balance shifts. The added pressure from the ocean can push saltwater further inland and upward into these aquifers, contaminating wells and reducing the availability of clean drinking water.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.

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