Q: How was Tahoe formed?
A: Although it is commonly believed that Lake Tahoe was formed by the collapse of a volcanic crater, the Basin was actually formed by the rise and fall of the landscape due to shifting of the geologic faults.

Blowing your top! About 2 million years ago, lava flowing from north shore's Mt. Pluto formed a barrier across the basin's northeastern outlet. Water from rivers and streams then filled the Lake Tahoe Basin over 600 feet highter than its present level!

Whose fault? Scientists estimate that about 5-10 million years ago tremendous forces began the western tilt of the Sierra Nevada block. Later the valley that became the Lake Tahoe Basin sank between two parallel faults as the mountains on either side continued to rise.

Rivers of Ice: A Daily Grind During the Ice Age, huge glaciers grew in the surrounding mountains. The broad U-shaped valleys of Emerald Bay, Fallen Leaf Lake and Cascade Lake were
carved by these rivers of ice.

Q: How large and deep is it?
A: Lake Tahoe is 22 miles long, 12 miles wide and has 72 miles of shoreline. Lake Tahoe's deepest point at 1,645 feet makes it the third deepest lake in North America and the tenth deepest in the world. The bottom of the lake is approximately 95 feet below the level of Carson City, NV.

Q: Why is it so blue?
A: The thin clear mountain air allows the lake's pure crystalline water to reflect the blue sky above. It can also appear red during sunsets or grey-black during storms.

Q: How clear is it?
A: Lake Tahoe is so clear in some places that objects can be seen to depths of 75'. Most of the snow and rain falls directly into the lake or drains through lakeside marshes and meadows that act as water filtering systems.

Q: Is Lake Tahoe's clarity threatened?
A: Yes. Although Lake Tahoe is going through a natural aging process, slowly filling in with sediments like other lakes, additional amounts are washed into the lake as slopes are cleared for construction. Each sediment particle carries nutrients that stimulate algae growth and could eventually cloud the famous clarity of the lake. Protecting the Lake's water quality is "job one" for the Forest Service at Lake Tahoe. Environmentally sensitive lands have been purchased and strict environmental standards adopted. Interagency monitoring programs continually test the water.

Q: Does it ever freeze?
A: No because the lake water is always in motion. Each winter the cold water on the surface sinks while warm water rises from the deep. This mixing motion keeps the lake from freezing over, though some protected inlets like Emerald Bay have been covered with a layer of ice.

Q: How much water is in the lake?
A: Over 39 trillion gallons. If completely drained, Lake Tahoe could cover a flat area the size of California to a depth of 14 inches, but would take over 700 years to refill.

Q: What's the elevation?
A: Lake Tahoe's average surface elevation is about 6,225 feet above sea level, making it the highest lake of its size in the United States. Its exact elevation depends on the amount of snowmelt and rainfall the basin receives. During drought the lake can drop below the rim of its natural outlet at Tahoe City and no water will flow out the Truckee River.

Q: How cold is the water?
A: The water in Lake Tahoe is very cold, ranging from 41 to 68 degrees Farenheit, depending upon depth and season. At 600 feet below the surface the temperature stays a constant 39 degrees Farenheit.