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.
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.
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.