On a bright day at Lake Tahoe, visitors marvel at the pristine cobalt waters of North America’s largest alpine lake, unaware of the looming threat. As wildfires rage across California in one of the state’s most severe fire seasons, an invisible danger is taking shape over these serene waters—wildfire smoke.
Traditionally, lakes like Tahoe haven’t been seen as particularly vulnerable to wildfires. After all, fire and water seem like natural opposites. Most conservation efforts to “Keep Tahoe Blue” have focused on combating the effects of mass tourism. However, recent research is shedding light on a concerning link between wildfires and lakes, specifically the smoke produced by these fires. Studies reveal that lakes across North America, including California’s cherished lakes, are increasingly exposed to wildfire smoke at unprecedented levels.
The Uncertain Impact of Smoke on Lakes
The long-term effects of this smoke exposure on lakes are still unclear, but scientists are sounding the alarm. The introduction of smoke can alter light and temperature conditions in lakes, disrupting ecosystems that rely on these elements for stability. Moreover, nutrient-rich ash falling into lakes could fuel the growth of harmful algae, further threatening these delicate environments.
“It could potentially change entire ecosystems,” warns Sudeep Chandra, director of the Global Water Center at the University of Nevada, Reno. He notes that lakes, already under tremendous stress from human activities and climate change, are now facing an additional threat from wildfire smoke.
Increasing Smoke Exposure in Lakes Across North America
California, a state significantly affected by climate change, is witnessing wildfires of growing frequency and intensity. In 2021, wildfires like the Park Fire burned vast swaths of land, exposing nearby lakes to weeks of smoke and ash. While researchers have long studied the impact of climate change on lakes, such as reduced snowpacks, the effects of wildfire smoke are only now coming into focus.
Recent studies using satellite data have uncovered alarming trends. For example, some lakes in California have experienced up to two months of smoke exposure in certain years. This phenomenon is not confined to California; nearly all lakes across North America have endured at least one “smoke day” annually between 2019 and 2021, with 90% experiencing more than 30 smoke days each year.
“Smoke has become more pervasive and extreme than in the past,” says Mary Jade Farruggia, an ecology graduate student at the University of California, Davis, and lead author of a study on this issue. Lakes that have never been affected by wildfires before are now grappling with the consequences.
The Ecosystem Fallout: Light, Temperature, and Nutrient Disruption
The full impact of wildfire smoke on lake ecosystems is not yet fully understood, but several key factors are at play. Thick smoke can block sunlight, leading to cooler water temperatures, reduced photosynthesis, and slower cellular respiration in aquatic plants and microbes. These changes can ripple through the food web, affecting everything from algae to fish.
Nutrient-rich ash, particularly from closer fire sources, can add significant amounts of nitrogen and phosphorus to lakes. This sudden influx of nutrients can disrupt normal cycles and fuel harmful algae blooms, as seen in Lake Tahoe during the 2021 Caldor Fire. Chandra points out that the composition and origin of the ash play a critical role, with finer ash deposited farther from fires potentially containing more key nutrients that stimulate algae growth.
Small mountain lakes, like California’s Castle Lake in the Shasta Mountains, are particularly vulnerable to the effects of wildfire smoke. These lakes, low in nutrients, can experience dramatic shifts in their ecosystems with the addition of nutrient-rich ash. In 2018, Castle Lake was covered in smoke for 55 consecutive days, resulting in significantly cooler water temperatures and increased algae levels due to reduced ultraviolet light penetration.
“Small lakes will be more sensitive and reactive to perturbations of any kind,” says Adrianne Smits, an aquatic ecosystem ecologist at the University of California, Davis. The changes in light conditions also impact fish behavior, with species like trout and salmon, which rely on light to hunt, potentially forced to relocate within the lake.
A Broader Environmental Crisis
California’s freshwater systems, already strained by human activity, diversions, and dams, now face the added stress of increased wildfire smoke. Despite this growing threat, the issue has yet to gain significant attention in policy discussions, with the focus remaining largely on the immediate human health effects of wildfire smoke.
“It’s an issue that hasn’t risen to the policy level yet,” says Patrick Wright, head of the California Wildfire and Forest Resilient Task Force. “But the fact that some of our most treasured ecosystems are at risk—it’s a really big deal.” Wright emphasizes the need for a holistic approach, considering entire watersheds, ecosystems, and forests in efforts to mitigate these emerging threats.
As wildfire smoke continues to affect lakes across North America, the urgency to address this environmental crisis grows. The future of Lake Tahoe and countless other lakes may depend on our ability to understand and mitigate these impacts before they cause irreversible damage.
