Average Secchi Disk Transparency
Average Secchi Disk Transparency
Average Secchi Disk Transparency
Meter (meters)
The annual average deep water transparency as measured by Secchi disk shall not be decreased below 29.7 meters (97.4 feet), the average levels recorded between 1967 and 1971 by the University of California, Davis.
This Indicator is reported in the following LT Info areas:
Average Secchi Disk Transparency
By: Data Average Method
Lake Tahoe is designated an Outstanding National Resource Water and a “Waterbody of extraordinary ecological or aesthetic value” by the states of California and Nevada, respectively, for its world famous clarity and striking blue color. Over the past half century however, clarity has significantly diminished. The Lake Tahoe TMDL Program seeks to effectively guide efforts to restore historic clarity within the lake so people may once again be able to see to depths of nearly 100 feet. Annual average Secchi disk depth measurements recorded at the Lake Tahoe Index Station (1968 through 2017). Each annual value is an integrated average using 18 to 37 individual measurements. The trend line (dashed line) is determined statistically using a general additive model (GAM) and used to assess long term trend in clarity. The TMDL Clarity Challenge target is a five year average of 23.8 meters (78 feet) by 2026. The five-year running average (red line) between 2012 and 2017 was 21.3 meters (70 feet).

 Transparency of Lake Tahoe as measured by the annual average Secchi depth.

Name Options
Data Average Method
Annual Average, 5-Year Average, Trend

Program Water Clarity


Measurements are taken in Lake Tahoe using a 25 centimeter, all white Secchi disk. The disk is lowered into the water column from a boat to a depth at which it is no longer visible by the observer, and then raised slowly until visible again. The midpoint of these two depths is called the Secchi depth. Between 18 and 37 individual Secchi depth measurements have been collected each year at an established index station. 

To download all of the water clarity data on this page please see Tahoe Open Data.


Associated Programs data not provided.