Fun Facts & History

Information provided by the U.S. Geological Survey and the U.S. Forest Service.

Why is it so blue?
Tahoe’s clean air and water are the keys to the Lake’s dazzling blue color. The surface of Lake Tahoe is blue in part because it’s reflecting the sky, but there is more to this phenomenon. Water as crystal clear as Tahoe’s absorbs red light, leaving the rich blue color that we all see.
How clear is the water?
Tahoe is so clear that in some places objects can be seen to depths of over 70 feet. One reason is that 40 percent of the precipitation falling into the Lake Tahoe Basin falls directly upon the Lake. The remaining precipitation drains through the 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. Read more about Tahoe's clarity.
Why is Tahoe losing clarity?
Recent water quality research has shed more light on the causes of the decline in lake clarity.  Lake Tahoe is experiencing a phenomenon known as cultural eutrophication — excessive algal growth due to excessive nutrient levels. Nitrogen and phosphorus from automobile emissions and urban and forested areas act like fertilizer to accelerate algal growth.

Aside from the negative impacts of nitrogen and phosphorus, scientists have identified fine sediments as the primary source of lake clarity loss. Fine sediments are tiny, ground up particles — much smaller than the width of a human hair. These fine sediments enter the lake from roadways and urban areas. Rather than falling to the bottom of the lake, fine sediments remain suspended in the water column, making the near shore areas appear murky and brown. Read more.
How was the lake formed?

The lake was formed through faulting of the Earth's crust, volcanism and glaciation.

About 25 million years ago the Sierra Nevada block was formed by tremendous uplifting. The valley that later became the Tahoe Basin sank between two parallel faults as the mountains on either side rose. Water filled this Basin where Lake Tahoe lies today.

Lava flowing from Mt. Pluto on the north shore formed a barrier or dam across the basin's outlet. Water from rivers and streams flowed into the Basin gradually filling it several hundred feet above its present level.

During the last Ice Age, less than a million years ago, huge ice blocks or glaciers formed in the surrounding mountains. These glaciers scoured the landscape, carving broad U-shaped valleys now occupied by Cascade Lake, Fallen Leaf Lake, and Emerald Bay. The material left after the glaciers melted, called moraines, blocked the original outlet of Lake Tahoe, changing it to the present Truckee River outlet at Tahoe City.

Where does the water go?
There are 63 streams that flow into Lake Tahoe and only one, the Truckee River, that flows out into Pyramid Lake. Unlike most bodies of water in North America, Tahoe's water never reaches the ocean.
How much water is in the lake?
The water in Lake Tahoe could cover a flat area the size of California to a depth of 14 inches. This is enough to supply everyone in the United States with 50 gallons of water per day for five years. And believe it or not, the amount of water that evaporates from the surface of Lake Tahoe every year could supply a city the size of Los Angeles for five years.
How cold is the water?
Waters are so cold in Lake Tahoe, staying a constant 39 degrees Fahrenheit below 600 feet. However, shallow areas around the lake can warm up to 60 degrees Fahrenheit during the summer months.
Does it ever freeze over?
The Lake Tahoe Basin has its share of below-freezing days and nights, but surprisingly enough the Lake itself has never frozen over. On occasion, Emerald Bay has been covered with a layer of ice, and ice also forms in cold protected inlets. However, Lake Tahoe's great depth and volume of water is always in motion and keeps it from being the world's largest ice rink.
How large is the lake?
Lake Tahoe is 22 miles long, 12 miles wide, and has 72 miles of shoreline. The surface area covers 191 square miles. Lake Tahoe's greatest depth of 1,645 feet makes it the second deepest lake in the United States, after Crater Lake in Oregon. The bottom of the Lake is 92 feet below the level of Carson City, Nevada.
What is the elevation?
Lake Tahoe's natural rim is is 6,223 feet above sea level, and its dam allows for a maximum surface elevation of 6,229 feet, making it the highest lake of its size in the United States. At any given time, its exact elevation is controlled by a dam at Tahoe City, and depends on how much water flows in from the mountains and how much is let out into the Truckee River.

For many thousands of years, Lake Tahoe was occupied only by Native American tribes. Artifacts confirm the presence of the Washoe Tribe of Native Americans at Lake Tahoe over 10,000 years ago. Native Americans camped, hunted, and fished at Lake Tahoe in relative seclusion until General John C. Fremont's exploration party "discovered" the lake in 1844.

For many years following Tahoe's discovery the area was virtually ignored. In 1859 however, the Comstock Lode was discovered in Virginia City, Nevada. During the 1860s Tahoe became the center of a lively commerce involving the silver mines in Virginia City and the Central Pacific Railroad (which was pushing over the Sierra toward the town of Truckee). The Comstock era resulted in large-scale deforestation of the Tahoe Basin, as timber was required to build mine shafts and support growing developments. It is estimated that over 80 percent of the Basin's forests were clear cut during this time.

Since then, public appreciation of Lake Tahoe and its natural resources has grown. During the 1912, 1913, and 1918 congressional sessions, conservationists made efforts to designate the Tahoe Basin as a national park but they were unsuccessful. Development pressures escalated again in the 1940s and 1950s, and a group of residents and visitors who were concerned about the environmental health of the region formed the League to Save Lake Tahoe.


Although it is commonly believed that Lake Tahoe is volcanic in origin, the Lake Tahoe Basin was actually formed by geologic block faulting 25 million years ago. Uplifted blocks created the Carson Range on the east and the Sierra Nevada Range on the west. Down-dropped blocks created the Lake Tahoe Basin in between.

A lake formed in the basin between the two ranges and was originally significantly larger than modern Lake Tahoe. Several active volcanoes poured lava into the basin, eventually damming the outlet near the present town of Truckee. The waters rose to several hundred feet higher than present level. Finally, a new outlet was cut, just east of Mt. Pluto (the present location of Northstar Ski Area). Modern Lake Tahoe was shaped and landscaped by the scouring glaciers during the Ice Age (the Great Ice Age began a million or more years ago). Moraines, glacial debris left behind, blocked the outlet again, changing it to the present Truckee River outlet at Tahoe City.

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