Short Wave The world’s freshwater is getting saltier. Why?
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Mar 25, 2026 A look at why freshwater is getting saltier around the world and the human activities driving it. Stories from local lakes reveal long-term salinity trends and hidden sources like road salt, fertilizer runoff, and seawater intrusion. The show explores ecological harms, threats to drinking water, the stubborn persistence of salt, and practical community strategies to cut salt use.
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Road Salt Has Long Term Cumulative Effects
- Freshwater salinity is steadily rising in many places because decades of road salt accumulate in nearby lakes and groundwater.
- Hilary Dugan's study found roughly half of hundreds of northern U.S. and Canadian lakes showed increasing salinity linked to salted roads nearby.
Multiple Human Sources Drive Freshwater Salting
- Other major salt sources include fertilizer runoff, mining, and seawater intrusion from overpumping aquifers.
- Seawater intrusion occurs when coastal aquifers are depleted and ocean water flows into groundwater supplies.
Modest Salinity Shifts Harm Native Aquatic Life
- Small increases in chloride can be toxic or stressful to freshwater organisms, favoring invasive species.
- Lake Wingra's current levels have been shown to harm fish, snails, and zooplankton while invasive species often tolerate higher salinity.