Lake Tahoe’s annual check-up is a scientific ritual that’s been going on since 1968. A UC Davis team of dedicated researchers plays doctor to our stunning Alpine lake, taking its temperature, checking its clarity, and basically giving it a full physical every year.

One of the stars of these reports is the lake’s famous clarity, measured by lowering a Secchi disk (a white, dinner plate-sized disk) into the water until it disappears from view. In the 1960s, the disk could be seen at a depth of 100 feet. Nowadays, sight of the disk disappears after about 60 to 70 feet.

Researchers pay close attention to the lake’s mixing patterns. Every winter, the surface water gets cold enough to sink and mix with deeper waters, which refreshes the lake’s oxygen supply. In some years, though, the lake doesn’t mix completely, leading to scientific head-scratching and concerned notes in the report.

Climate change is mentioned frequently in the reports. With the lake’s surface waters warming over the years, everything from the mixing patterns to the types of algae in the lake have been affected.

Then, there are the invasive species. It’s an ongoing saga of protecting the lake from Asian clams, Asian carp, and quagga mussels, just to mention a few.

The reports also track the lake’s “beach health,” which is essentially a scientific way of saying “how nice is it to spend a day at the beach?” This includes monitoring everything from algae washing up on shore to the presence of bacteria that might make swimmers think twice about taking a dip. 

Perhaps the best aspect of these reports is how they capture the lake’s personality quirks from year to year. Some years, the lake is remarkably clear; other years, it’s a bit cloudier. Sometimes it mixes well, other times it’s lazy about it. It’s like reading an annual newsletter about a temperamental 1,645-foot-deep lake.

For instance, did you realize that the daily evaporation from Lake Tahoe (half a billion gallons) would meet the daily water needs of 5 million Americans? Or, that a single Daphnia (water flea to most of us) can consume 100,000 fine particles every hour, or that, worldwide, there is not one large lake that exceeds Lake Tahoe’s annual clarity? The full report can be found at https://tahoe.ucdavis.edu/stateofthelake. It’s worth a read. 

The University of California, Davis team has essentially become Lake Tahoe’s biographers, documenting everything from its surface temperature tantrums to its deepest mixing moods. These reports serve as yearly chapters in the ongoing story of one of America’s most treasured lakes, helping us understand how to keep this azure jewel of the Sierra Nevada sparkling for generations to come.