Warmer water provides a more hospitable environment to algae and invasive species. Lake Tahoe's waters are already warming. Lake Tahoe's water was recorded by researchers at the University of California at Davis Tahoe Environmental Research Center at 68.4 degrees Fahrenheit in 2017. That is the highest average daily reading ever recorded of the Lake's waters since temperatures were first mesured in 1968. In the last four years alone, the average temperature of the Lake at all depths has increased by an average of 0.26 of a degree a year — a rate 10 times greater than the long-term warming rate, the researchers found.
Average air temperatures at Tahoe have also risen more than two degrees since a continual record began in 1911. Spring snowmelt occurs an average of two weeks earlier than in the early 1960s. (UC Davis-TERC State of the Lake 2016)
More rain, less snowIn the coming decades, scientists predict more rain and less snow will fall in Tahoe, and there will be more flood-causing storms where rain falls on snow. Snow has already decreased from an average of 51 percent of total preciptation in 1910 to 33 percent of total precipitation today. Scientists at UC Davis are predicting air temperatures could rise by as much as 9 degrees by 2100.
These dramatic changes have ski resorts concerned because as winters grow warmer, the elevation at which precipitation turns from rain to snow will creep higher and higher up the mountainside, impacting their businesses.
Scientists also expect California to experience an increase in extreme precipitation events. Streams and rivers will flow with greater intensity during these rainstorms, causing more fine sediment to flow into the Lake. Property ownersat Tahoe can help minimize the effects of these storms by installing mandated erosion and runoff control measures.
When they first started measuring Lake Tahoe's water clarity in 1968, researchers could see a special white plate, known as the Secchi disk, 102.4 feet below the surface. But that’s not the case anymore. According to UC Davis researchers, in 2017, clarity dropped by 16.7 feet to 56.4 feet as tiny algae amassed in the lake’s upper reaches, clouding the view. As Lake Tahoe warms, the League is concerned that loss of clarity could be a byproduct. Our efforts focus on ensuring that Lake Tahoe remains resilient in the face of these changes.
Scientists with the Tahoe Environmental Research Center have identified one particularly concerning outcome from the warming trend.
"What we expect is that deep mixing of Lake Tahoe's water layers will become less frequent, even non-existent, depleting the bottom waters of oxygen. This will result in major, permanent disruption to the entire lake food web," researcher Geoffrey Schladow told Science Daily in 2008.
"This is not unheard of," he told the publication. "Anoxia (oxygen depletion) occurs annually in most lakes and reservoirs in California in the summer. But Tahoe has always been special. It's been above and beyond such things.
"A permanently stratified Lake Tahoe becomes just like any other lake or pond. It is no longer this unique, effervescent jewel, the finest example of nature's grandeur."
The cold water at the bottom of the Lake (below 100-150 meters) has typically mixed with the surface water, on average, about once every four years.
As the surface water continues to increase in temperature, the extent and frequency of deep mixing could change. In as little as a decade, the Lake may no longer experience deep mixing.
Without the mixing, oxygen would become depleted in the deep water, creating an uninhabitable environment for many aquatic species, including recreational fish species. In addition, without any oxygen near the bottom of the lake, the plant material that sinks from the surface would not undergo typical bacterial breakdown. Consequently, the bottom of the lake would become nutrient-laden and phosphorus-rich.
Schladow told Science Daily that when the oxygen is gone, phosphorus that is currently locked up in the lake-floor sediments will get released. This phosphorus will eventually reach the Lake's surface, where it will fuel algae growth. Algae blooms can cause many problems, including reduced lake clarity, unpleasant odors and bad-tasting drinking water. Blooms of blue-green algae can even release toxins that are harmful to people and wildlife.