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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Watershed Priorities

Lake Tahoe TMDL

Historic Agreement to Improve Lake Tahoe Water Quality (News Release)

Lake Tahoe TMDL overview and resources

Lake Tahoe
Lake Tahoe Clarity Commitment | Enlarge
Presidential Commitments to Lake Tahoe: EPA Fulfills Promises

In 1997, Executive Order 13057 was signed directing federal departments and agencies having principal management or jurisdictional authorities in the Lake Tahoe Region to establish a Federal Interagency Partnership. The purpose of the partnership was to implement meaningful actions at Lake Tahoe to improve water quality, transportation, forest management, recreation and tourism, and to protect Lake Tahoe's environment. To accomplish the objectives of the Executive Order, 39 actions were developed known as Presidential Commitments. EPA is responsible for 12 of these 39 Commitments and has fulfilled all of them.

Read more about EPA's Presidential Commitments (PDF) (3 pp, 19K) and the Lake Tahoe Federal Interagency Partnership (PDF) (16 pp, 1.3MB)

Lake Tahoe, California and Nevada

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Ancestral inhabitants of the Lake Tahoe area - the Washoe tribe Exiting EPA (disclaimer) - called the Lake "Da ow a ga," which means "edge of the lake;" the tribe considers Lake Tahoe as a sacred life-sustaining water, and the center of the Washoe world.

Lake Tahoe is one of the largest, deepest, and clearest lakes in the world. Its cobalt blue color, biologically diverse alpine setting and remarkable water clarity is legendary. In 1872, American writer, Mark Twain, described Lake Tahoe as ". . . a noble sheet of blue water lifted six thousand three hundred feet above sea level and walled in by a rim of snow-clad mountain peaks that towered aloft full three thousand feet higher . . . I thought it must be the fairest picture the earth affords."

Lake Tahoe Fast Facts:

  • Lake Tahoe is 2 million years old
  • Size of watershed: 501 sq. miles
  • Lake surface area: 192 sq. miles 1,645 ft. deep
  • 6,223 ft. elevation (natural rim)
  • 2 states: CA, NV
  • 5 counties, 1 city
  • 50,000 Tahoe Basin year-round residents
  • Majority of private property owners are part-time residents
  • US Forest Service Exiting EPA (disclaimer) and state agencies manage almost 85% of land area
  • Average surface water temperatures are 68° Fahrenheit in the summer and 41° in the winter
  • 63 streams feed into Lake Tahoe but only one, the Truckee River, flows out
  • Approximately 3 million people visit Lake Tahoe every year
  • The Lake is designated as an Outstanding National Resource Water under the Federal Clean Water Act
  • Lake Tahoe is the second deepest lake in the United States
  • Lake Tahoe is so deep that a single drop of water entering the Lake today will take about 650 years to find its way out

In addition to being a scenic and ecological treasure, the Lake Tahoe Basin is one of the outstanding recreational resources of the United States. It is recognized nationally and globally as a natural resource of special significance. The communities and the economy in the Lake Tahoe Basin depend on the protection and restoration of its stunning natural beauty and diverse recreational opportunities in the region.

Water Quality Issues

Lake Tahoe can be differentiated into two zones: deep-water and nearshore. Monitoring data indicate a decline in the water quality of both zones. Since 1968, deep-water clarity has been reduced by approximately 30%, from 100 to 66 feet. Similarly, the nearshore environment has experienced degraded conditions due to proliferation of algae and other aquatic invasive plants and animals, particularly in urbanized areas.

The decline in Lake Tahoe's water clarity is a result of fine sediment particles and phytoplankton (algae). Fine sediment particles are the most dominant pollutant contributing to the impairment of the lake's deep water transparency, accounting for roughly two thirds of the lake's impairment. Inorganic fine sediment particles less than 16 micrometers (about 1/3 the diameter of a human hair) are the main pollutant that is degrading deep-water clarity. However, nutrients also play an important role, particularly with respect to the nearshore condition.

Because these three pollutants are responsible for Lake Tahoe's deep water transparency loss, Lake Tahoe is listed under Clean Water Act Section 303(d) as impaired by input of nitrogen, phosphorus, and sediment. The goal of the Lake Tahoe Lake Tahoe TMDL (total maximum daily load) is to set forth a plan to restore Lake Tahoe's historic deep water transparency to 29.7 meters (97.4 feet) annual average Secchi Depth by 2076. Deep water transparency and Secchi depth refers to how scientists measure how clear the lake water is; basically, a round disk is lowered from a boat into the water until it is no longer visible. At the point it is no longer visible, the length of the rope/cable used to lower the disk is the transparency recorded.

Primary discharge sources of fine sediment, nitrogen, and phosphorus into Lake Tahoe:

  • Urban uplands runoff
  • Atmospheric deposition
  • Forested upland runoff
  • Stream channel erosion

Other issues:

  • Destruction and alteration of wetlands
  • Fire suppression and periodic drought resulting in approximately 25 percent of trees dead or dying
  • Threat of catastrophic fire and insect infestation; loss of biological diversity
  • The establishment and threat of aquatic and terrestrial invasive species, such as the Asian clam and quagga mussel

Climate Change

Global climate change is projected to have unprecedented impacts on the health of the environment and economy in the Lake Tahoe Basin. As temperatures rise and more precipitation falls as rain rather than snow, management efforts to protect the Basin's forests, fish and wildlife, and fabled water clarity will face unique challenges.

The State of the Lake Report 2013 released by the Tahoe Environmental Research Center, UC Davis Exiting EPA (disclaimer) suggests that climate change may have produced conditions which favor the proliferation of Cyclotella, a single-cell, free-floating algae, which in large concentrations can diminish clarity.

To address these and other impacts, the Environmental Improvement Program (EIP) partner agencies are formulating a Basin-wide strategy to address climate change. The strategy is intended to ensure that all major planning and regulatory programs at Lake Tahoe are designed to take into account the projected impacts of climate change. For example, future water quality and erosion control projects may need to be designed for larger peak flows in the winter, and habitat improvement projects may need to take into account potential changes in the type, location, and distribution of vegetation communities.

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