After wildfires burn in the western United States, the water quality of nearby streams, rivers, and lakes worsens — and often remains poor for longer than originally thought — according to a new study published last week in the journal Nature Communications Earth & Environment.

The study, led by researchers at the University of Colorado Boulder, found that “contaminants like organic carbon, phosphorus, nitrogen, and sediment can degrade water quality for up to eight years after a fire.” The scientists explain that unburned forests, lush with vegetation, serve as natural sponges and filters for rainwater when it falls. Trees, plants, and soils soak up water, limiting runoff. But fire consumes vegetation and cooks soils, making the ground hydrophilic. Rainfall after a burn moves quickly across the forest floor, collecting ash, sediment, and other contaminants and organic matter and depositing them into fresh water bodies, where they have lasting effects on water quality.

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