When a rainstorm swept over the scorched hillsides left by the 2022 McKinney Fire, it seemed like relief was finally arriving. Instead, dissolved oxygen in the Klamath River collapsed to zero — and stayed there for more than five hours. Fish died along nearly 60 miles of one of California’s most culturally significant waterways.
Rain was supposed to help. A new USGS study, the first of its kind, documents how it didn’t.
A storm that made things worse
The McKinney Fire ignited in late July 2022 in Siskiyou County, becoming the largest wildfire in California that year. It left thousands of acres of scorched hillslopes — bare, unstable ground with little vegetation to slow runoff. When a high-intensity rainstorm followed, water moved fast across that burned landscape, picking up everything in its path.
What it carried into the Klamath River was devastating. Stormwater flushed ash, charcoal, and sediment from the fire scar directly into the waterway. Dissolved oxygen dropped to zero — a condition scientists call anoxia — and held there for more than five hours. Fish had no way to survive it. Aquatic life died along nearly 60 miles of river, including juvenile salmon already navigating one of the most challenging migration corridors in the American West.
How fire scars turn rain into a threat
The damage didn’t happen all at once. According to the USGS study, the event unfolded in two distinct waves: an initial flood surge that moved quickly downstream, then a second, more dangerous pulse — a concentrated load of ash, charcoal, and sediment scraped from freshly burned hillslopes.
That organic material doesn’t just cloud the water. As it decomposes, it consumes dissolved oxygen, stripping the river of what fish need to breathe. The more material that enters, the faster oxygen disappears.
Vegetated hillslopes absorb and filter runoff. Burned ones don’t — they produce far more extreme runoff and deliver far more oxygen-consuming material in a single event. That’s what makes rain-on-wildfire collisions so dangerous, and so different from typical flood events. This study is the first published research to directly link such an event to lethal water-quality conditions in a large river.
Sensors that caught what the eye could not
No one watching the Klamath River that day would have seen the oxygen disappear. The water looked bad — turbid, dark with ash — but the invisible collapse of dissolved oxygen required instruments to detect.
Continuous, high-frequency monitoring sensors made the documentation possible. Stations along the river tracked turbidity, dissolved oxygen, pH, conductivity, and temperature across the full arc of the event. That real-time data let scientists reconstruct exactly what happened and when — something eyewitness observation alone never could have captured.
Those stations weren’t operated by USGS alone. The Karuk Tribe and the Yurok Tribe jointly ran monitoring infrastructure alongside federal scientists. Researchers suggest the scarcity of documented post-wildfire anoxia events likely reflects a monitoring gap rather than a rarity of occurrence. Without continuous sensors already in place, events like this simply go unrecorded.
A river at the center of a culture
The Klamath River is not just a waterway. For the Karuk and Yurok Tribes, it’s a living system tied to identity, food sovereignty, and generations of ecological stewardship. Salmon are central to both cultures — and both Tribes have long understood that the river’s health is inseparable from their own.
Toz Soto, Fisheries Program Manager for the Karuk Tribe Department of Natural Resources, noted that fire frequency, size, and burn intensity are all increasing — making it more urgent to understand the risks to native fish populations and water quality. The Karuk Tribe, he said, is committed to long-term water-quality monitoring to keep learning about large fires and floods.
Yurok Tribe Environmental Department Water Program Manager Josh Cahill echoed that commitment. Through the partnership with USGS, he said, the Tribes can track the Klamath River’s ever-changing conditions in real time.
What comes next as wildfires intensify
The conditions that produced this event are becoming more common. Wildfires across the western United States are growing more frequent and more severe, while late-summer monsoon storms are intensifying — raising the probability that the two will collide over freshly burned land.
The Klamath River basin is already feeling that pressure. Despite being California’s wettest region, it’s seeing significant increases in fire size, severity, and frequency.
The USGS study calls for expanding continuous, high-frequency monitoring in fire-prone watersheds. Anoxia can develop and pass within hours — short-lived enough that it’s nearly impossible to document without sensors already in the water. The Klamath basin partnership offers a working model: Tribal knowledge, federal science, and real-time data combined to protect a river that can’t afford to go unobserved.