I was standing by Lake Coeur d’Alene on a fall day, taking in the beautiful view, when a woman passing by asked me, “Has the lake turned over yet?” 

I gave her a vacant look, smiled and said “no,” having no idea what I was saying “no” to. “Turn over” was what you did to pancakes, and no spatula I’ve ever seen could turn over a lake! 

A little digging explained what she was asking. She wanted to know if the lake had reached the tipping point where cold air temperatures made the lake’s surface water temperature equal to the water at the bottom of the lake. When the water from top to bottom is the same temperature, the lake water mixes throughout the layers and the lake will “turn over.” 

Her simple question is a window into the future of our beautiful lake. “Turning over” is just one part of an annual cycle that starts with the lake uniformly cold in winter. 

Spring’s sunshine and warming air temperatures warm the lake's surface water creating a layer of warmer, lighter water that floats on top of the colder, heavier water deeper down. This layering effect or “stratification” strengthens with the summer sun and hot weather and prevents the oxygen in the surface water from mixing downward, resulting in less oxygen in deeper water than in surface water. With fall and winter’s colder weather, the lake’s surface waters cool and eventually become colder and heavier, and the lake will “turn over” and become uniformly cold for the winter. Cycle complete!  

As our winters get steadily warmer and we receive more winter rain and less snow, the water entering our lake is warmer. The combination of warmer spring air temperatures and warmer water temperatures results in longer periods of stratification. 

Warming temperatures will also increase the length of the growing season for algae and rooted plants. This alters the base of the lake’s food web and can create nuisance plant and algae growths. Algae that grow in this warm surface layer will eventually die and sink to the lake bottom. Bacteria will then decompose the dead algae, consuming oxygen in the process. Combine this with longer periods of lake stratification; the lake’s bottom waters will have less oxygen and be less habitable to life, especially for cold-water adapted species like cutthroat and bull trout.  

Lower oxygen levels in the lake’s bottom waters will also change the chemistry in the lake’s sediments in ways that release more nutrients as well as contaminants in sediment (lead, arsenic, cadmium and zinc) from this region’s legacy mining activities. The combination of more nutrients and temperature shifts will increase the frequency and duration of toxic algae blooms and lead to a decline in native trout species.  

We have all noticed a warmer Coeur d’Alene over the last few years. This has greater impacts than what the casual observer sees. What’s obvious is the hotter summer days, the increased presence of wildfire smoke, more winter rain and less snow. What isn’t obvious is this combination of factors that impacts our lake’s health. It’s this lake that adds so much to the beauty of our area and is the engine that drives our local economy.  

What can we do with such a large-scale concern, though? Fortunately, there are simple ways we can all decrease our contribution to climate change in everyday activities. For example, we can lower transportation-related emissions by working from home a day a week if our jobs allow it, carpooling, driving less aggressively and minimizing cargo hauling on vehicle roofs. Burning 1 gallon of gas produces 20 pounds of CO2, so every bit of fuel efficiency is helpful. 

For more information and ideas on what we can do individually and as a community, please go to the Kootenai Environmental Alliance website to read the Coeur d’Alene Climate Adaptation Project report at https://funnels.kealliance.org/ccap.

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Dave Muise is vice president of the Kootenai County Enviornmental Alliance board. 

The Our Gem Coeur d’Alene Lake Collaborative is a team of committed and passionate professionals working to preserve lake health and protect water quality by promoting community awareness of local water resources through education, outreach, and stewardship. Our Gem includes local experts from the University of Idaho - Idaho Water Resources Research Institute, Coeur d’Alene Tribe, Idaho Department of Environmental Quality, the Basin Environmental Improvement Project Commission, Kootenai Environmental Alliance, Coeur d’Alene Regional Chamber of Commerce, and Kootenai County.