Wildfires impact Western water quality for up to 8 years

June 23, 2025 — Wildfires can contaminate rivers and streams across the Western United States for years after the flames are extinguished, according to a new study published Monday in Nature Communications Earth & Environment.

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Researchers from the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder analyzed more than 100,000 water samples from 500 river basins, making it the first large-scale assessment of post-wildfire water quality across the West.

The team found elevated levels of organic carbon, phosphorus, nitrogen and sediment in rivers as long as eight years after fires. Half of the samples were collected from burned basins and half from unburned sites, allowing scientists to compare changes over time.

“We were attempting to look at notable trends in post-wildfire water quality across the entire U.S. West, to help inform water management strategies in preparing for wildfire effects,” said Carli Brucker, lead author and former doctoral student at CU Boulder and Western Water Assessment.

Contaminants such as organic carbon, phosphorus and turbidity were significantly elevated in the first one to five years after a fire. Nitrogen and sediment levels remained high for as long as eight years, particularly in forested regions. The study found that watershed recovery takes longer than previously believed.

Researchers used data-driven models to evaluate water quality changes before and after wildfires, calculating averages across burned and unburned basins.

“It can take two years, up to eight years, for the effect to be fully felt,” said co-author Ben Livneh. “Sometimes it can be a delayed effect, meaning it’s not all happening right away, or sometimes you need a big enough storm that will mobilize enough of the leftover contaminants.”

The findings provide water managers with critical data to help plan for wildfire impacts and improve response strategies.