USGS Science in the Lake Tahoe Basin

Lake Tahoe is a beautiful Alpine Lake in the Sierra Nevada on the border of California and Nevada. Known for its deep, clear water, Lake Tahoe is the second deepest lake in the United States, with a maximum depth of 1,645 feet. The average depth of Lake Tahoe is 1,000 feet.

Lake Tahoe has the clearest water of any large lake worldwide. Lake clarity is measured using a method called the Secchi depth: a 8-10 inch white Secchi disk is lowered into the water and the deepest point at which the disk can be seen is the known as the Secchi depth. In 2015, the Tahoe Environmental Research Center (TERC) reported the Secchi depth of Lake Tahoe to be 77.8 feet. Lake Tahoe clarity had been declining by nearly a foot a year for nearly five decades; however, winter Secchi depths have been improving the last ten years (2006 - 2016), and the annual average clarity of the lake over this decade was slightly better than the prior decade (1996 - 2006; State of the Lake Report 2017). In 2016, the annual average clarity was 69.2 feet; over 5 feet deeper than in 1997, but farther from the clarity restoration goal of 97.4 feet. Many factors contribute to lake clarity including algal growth from increased nutrients in the lake and suspended sediment being transported to the lake by streams.

Sixty-three tributaries flow into Lake Tahoe; however, the Truckee River is the only stream to flow out of Lake Tahoe. The Truckee River flows northeast from the Lake through Reno, Nevada, and continues to its terminal discharge at Pyramid Lake. The upper 6 feet of Lake Tahoe is used as a storage reservoir for the Truckee River Basin. The amount of storage within the Lake and the release to the Truckee River is controlled by a dam at Tahoe City. Legal agreements require that Lake Tahoe be maintained at an altitude between 6,229.1 feet and 6,223 feet (the natural rim). During drought conditions, the Lake can fall below the natural rim.

The Nevada Water Science Center (NVWSC) has been involved in measuring streamflow, ground-water levels, lake levels, and stream, lake, and groundwater quality in the Lake Tahoe Basin since the late 1970’s. USGS currently (2018) maintains 9 streamflow gaging stations on tributaries to Lake Tahoe and 1 gaging station on the outflow channel from the lake. Four gaging stations are maintained by NVWSC and six stations by the California Water Science Center.

Lake Tahoe Nearshore Periphyton

USGS and the University of Nevada-Reno, in cooperation with the Lahontan Regional Control Board, investigated the cause of changing periphyton biomass in the nearshore environment of the lake at Ward Creek, near Tahoe City. Chemical and physical characteristics of the lake, Ward Creek, and shallow groundwater were studied to determine their influence on nearshore periphyton growth.

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Lake Tahoe Interagency Monitoring Program

The Lake Tahoe Interagency Monitoring Program (LTIMP) is a partnership between USGS, U.C. Davis, the Tahoe Regional Planning Agency, Lahontan Regional Water-Quality Control Board, and the California Tahoe Conservancy. Started in 1979, LTIMP supports the collection of streamflow and water-quality data at numerous tributaries around the lake to determine trends and estimate nutrient and sediment loads to Lake Tahoe.

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Lake Tahoe Research Highlights

For decades, USGS has been involved with a wide range of scientific research and monitoring activities in the Lake Tahoe basin. Research activities cover topics such as the potential response of snowpack to climate change, wildfire influences on birds or water quality, changes in landscape due to human activity, and natural hazards. Monitoring the level and quality of streams, groundwater, and lake provide the baseline information needed for hydrologic research and continued water-resource management.

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The current lake elevation can be calculated by adding the gage height from the graph below to 6,220. The natural rim of Lake Tahoe is 6,223 ft and the maximum legal limit is 6,229.1 ft (Bureau of Reclamation datum). Use the cursor below the graph to change the time scale.

Lake of the Sky is a documentary movie highlighting USGS research in the Lake Tahoe Basin. The movie features USGS science conducted by hydrologists, geologists, geographers, computer modelers, and biologists, among others. The story is told through the use of narration, expert interviews, graphics, animations, incredible video imagery and time-lapse video. USGS science detailed in the story includes water-quality monitoring, streamgaging, Lake Tahoe bathymetry, aerial LiDAR, historic use of aerial photography, and the Tahoe Land Use Simulation Model. This wide range of consistent, reliable, long-term data and maps are crucial for evaluating and managing the lake and surrounding basin.

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USGS Data on Lake Tahoe

USGS data for Lake Tahoe Basin, including data from the Lake Tahoe Data Clearinghouse are now available on the Data page.