Warmer water provides a more hospitable environment to algae and invasive species. Lake Tahoe's waters are already warming. On average at the surface, Lake Tahoe's water was 53.3 Fahrenheit in 2015, the warmest since UC Davis researchers began keeping a continuous record in 1968.
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 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 owners at Tahoe can help minimize the effects of these storms by installing mandated erosion and runoff control measures.
Lake mixingScientists 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.