Data released April 7, 2015 by the UC Davis Tahoe Environmental Research Center and the Tahoe Regional Planning Agency showed that the average annual clarity level for 2014 is at 77.8 feet. That is the depth at which a 10-inch white disk, called a Secchi disk, remains visible when lowered into the water. This represents a 7.5 foot increase over the previous year and is almost 14 feet greater than the value of 64.1 feet in 1997, when the lowest average clarity value was recorded. [1]
Organizations Focused on Lake Tahoe Water Clarity
The Tahoe Regional Planning Agency leads the collaborative effort to reduce stormwater runoff and manages the multijurisdictional Lake Tahoe Environmental Improvement Program to repair past damage to the ecosystem.
Over the past two decades, the Environmental Improvement Program has resulted in substantial public and private investment in projects to improve water quality and other environmental indicators at Lake Tahoe. Among the hundreds of measurements the TRPA tracks, mid-lake clarity is a key indicator of whether restoration programs are working. [1]
Factors Affecting Clarity
One reason Lake Tahoe is so clear is that 40 percent of the precipitation falling onto the Lake’s watershed falls directly upon the Lake. The remaining precipitation drains through marshes and meadows, which are a good filtering system for water. Unfortunately, many of the Lake's natural filtering systems have been disturbed by development and Tahoe's clarity is diminishing. Scientific measurements of water clarity started in 1968.[2] Information about environmental factors affecting Lake Tahoe are included in the annual State of the Lake Report.
Annual average clarity readings since 1997
Water clarity measurements have been taken continuously since 1968, when the Secchi disk could be seen down to 102.4 feet, and is one of the longest, unbroken clarity records in the world. Secchi depth is the most widely used method of clarity measurement, and the values are in agreement with the laser-based measurements that are also taken by TERC researchers. While the average annual clarity in the past decade has been better than in preceding decades, it is still short of the clarity restoration target of 97.4 feet set by federal and state regulators. [3]
- 2014: 77.8 feet
- 2013: 70.2 feet
- 2012: 75.3 feet
- 2011: 68.9 feet
- 2010: 64.4 feet
- 2009: 68.1 feet
- 2008: 69.6 feet
- 2007: 70.1 feet
- 2006: 67.7 feet
- 2005: 72.4 feet
- 2004: 73.6 feet
- 2003: 71.0 feet
- 2002: 78.0 feet
- 2001: 73.6 feet
- 2000: 67.3 feet
- 1999: 69.0 feet
- 1998: 66.1 feet
- 1997: 64.1 feet
References
1. Water clarity levels improve in Lake Tahoe, Phys.org, April 08, 2015.
2. Tahoe's Unique Clarity, League to Save lake Tahoe, Accessed April 9, 2015.
3. Lake Tahoe water clarity in 2014 the best in more than a decade, news.ucdavis.edu, April 7, 2015.
