Lake Tahoe Facts You May Not Have Known

You may already know a few basic facts about Lake Tahoe, such as:

• The lake straddles the California/Nevada border

• Tahoe is the largest alpine lake in North America

But here are some more detailed facts you may not have known.

The age of Lake Tahoe

Lake Tahoe is over 2 million years old, which makes it an ancient lake. An ancient lake is one that has consistently held water for over a million years.

The depth of Lake Tahoe

We’ll do a little math to answer the question, "how deep is Lake Tahoe?"

The elevation at the deepest part of the lake is at 4,585 feet. That’s a lower elevation than Emigrant Gap, which is at 5,190 feet above sea level.

The legal limit for Lake Tahoe’s surface elevation is 6,229.1 feet. When necessary, a dam at Tahoe City spills lake water into the Truckee River to ensure the lake does not rise above this level.

Based on the above numbers, the maximum depth of the lake is 1,644.1 feet. However, the commonly published depth of Lake Tahoe is 1,645 feet. Either way, that’s the equivalent of a 125 story building.

The surface area of the lake

The shore length of Lake Tahoe is approximately 71 miles. The maximum length is about 22 miles and the maximum width is 12 miles. The surface area is 191 square miles.

The volume of water in Lake Tahoe

The lake holds about 39 trillion gallons of water. Depending on the water level, the volume can vary by almost 250 billion gallons.

Where the lake's water goes

As with many bodies of water, much of the water evaporates. About a third of the water goes into the above-mentioned Truckee River. The river flows through Truckee and Reno before terminating at Pyramid Lake in Nevada.

How clear is the water in Lake Tahoe?

This is a Lake Tahoe fact that a lot of people would like to see change.

The clarity (or transparency) of water is determined by submerging a small white disk called a Secchi disk into the water on a line. The depth at which the disk is no longer visible is used as a measure of the transparency of the water.

The University of California at Davis has continuously monitored the clarity of Lake Tahoe since 1968, when a Secchi disk could be seen 102 feet below the surface.

Since then, the overall trend has been progressively less transparency.

UC Davis Annual Average Secchi Depth

In 2017, clarity dropped to 60.4 feet, which was the least transparency ever recorded. In 2018, clarity rebounded to 70.9. However, the clarity dropped by almost 8 feet to 62.7 feet in 2019.

Does Lake Tahoe ever freeze?

Emerald Bay, a relatively shallow part of the lake, freezes in some years. The rest of the lake never freezes, with two minor exceptions.

Why? It's a function of the temperature of the lake's surface waters. Because Lake Tahoe has a high volume to surface area ratio, it does not lose nearly as much heat in the winter as a shallow lake does.

For a lake to freeze, its surface waters must first cool to 39°F. At this temperature, the surface waters become denser than the underlying waters. The surface water sinks below those underlying waters. This, in turn, leads to the [replaced] surface waters dropping to the freezing point.

Aside from Emerald Bay, Lake Tahoe’s surface waters temperature never drops to 39°F.