Discover Why Lake Tahoe Is So Clear and Blue

Written by Mike Edmisten
Updated: July 21, 2023
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Lake Tahoe was formed by volcanos, faulting, and glaciation over a span of 3 million to 4 million years, placing it among the 20 oldest lakes in the world. However, the Lake Tahoe Dam constructed in Tahoe City in 1913 raised the lake’s water level by approximately 10 feet, turning the naturally occurring lake into a reservoir.

An ancient lake, Lake Tahoe’s waters are clear in part due to a limited amount of algae.

Lake Tahoe’s Size

Straddling the border of Nevada and California, Lake Tahoe contains nearly 39 trillion gallons of water, giving it the sixth-largest volume of any lake in the United States. Only the five Great Lakes contain more water.

The average depth of the lake is 1,000 feet. It measures 1,645 feet at its deepest point, making it deep enough to submerge the Empire State Building (with almost 200 feet to spare!). Lake Tahoe is the second deepest lake in the United States, behind Crater Lake in Oregon. It is the third deepest lake in North America and the eleventh deepest in the world.

Lake Tahoe is 22 miles long and 23 miles wide, featuring 75 miles of shoreline. Located in the Lake Tahoe Basin in the Sierra Nevada mountain range, the lake’s elevation is 6,225 feet above sea level. It is the largest alpine lake in North America, leading to the nickname “Lake of the Sky.”

Lake Tahoe in Zephyr Cove, Nevada.

Lake Tahoe’s location in the Sierra Nevadas earned it the nickname “Lake of the Sky.”

©Trevor Fairbank/Shutterstock.com

Clear Blue Water

The water of Lake Tahoe is a stunningly clear cobalt blue. Mark Twain once described the lake as “a noble sheet of blue water.” He went on to say, “It must surely be the fairest picture the whole earth affords.” What makes the water of this alpine lake so pristine that it captured the imagination of Twain, along with millions of others? What creates the amazing clear blue water for which the lake has long been famous?

The blue color is partially a reflection of the sky. The lake’s crystal clear water absorbs red light, leaving the rich, lovely blue color that the human eye observes. The blue hue of the water also comes from the lack of algae in the lake, although that is changing. More on that in a moment.

The lake’s water is so clear that objects as deep as 65-70 feet can be seen from the surface. This incredible water clarity is the result of a few different factors. First, the lake is naturally nutrient-poor, hindering algae growth that would otherwise diminish the water’s clarity and blueness. Secondly, the lake’s sheer size means that 40% of the precipitation falling into the Lake Tahoe Basin falls directly into the lake itself. And third, the remaining precipitation that eventually flows into Lake Tahoe picks up very little particulate matter. The Lake Tahoe basin has a granite bedrock that doesn’t break down into fine particles as water runs over it. 

The runoff also drains through meadows and marshes, which naturally filter the water. As a result, whatever small amounts of particulate matter there may be in the runoff water are mostly removed before it reaches the lake.

Lake Tahoe

40% of precipitation in the Lake Tahoe Basin falls directly into the lake itself.

©Joseph Sohm/Shutterstock.com

The Lake Is Changing

However, as clear as the Lake Tahoe water is today, it was even clearer 50-plus years ago. In 1968, objects as deep as 100 feet could be seen from the lake’s surface. The meadow/marsh filtration system has been depleted due to manmade development around the 312-mile watershed of the basin. Many of the meadows and wetlands have been paved over with roads and parking lots. These paved areas greatly increase the stormwater runoff that flows into Lake Tahoe. This runoff carries fine sediment pollution into the lake and has significantly reduced the water’s clarity over the past five decades.

A Very Bad Idea

Another contributor to the loss of clarity is invasive shrimp. Mysis shrimp were purposefully added to the lake in the 1960s as a food source for native trout. This well-intentioned action had a boomerang effect, though. The tiny, translucent shrimp that measure less than an inch long have a lifespan of one to two years and reproduce with great speed. These minuscule shrimp now number in the billions in the lake’s waters and have nearly eaten to extinction ​​the native zooplankton that kept the water so clear and blue.

Before the introduction of mysis shrimp, zooplankton ate algae and sediment, keeping the lake waters clear and blue. The shrimp have now decimated the zooplankton of the lake, which has allowed algae growth to increase. This higher algal concentration has caused the lake’s blue clarity to diminish.

The original hope was that the natural fish of Lake Tahoe would eat the shrimp. As a result, the fish would grow larger, and those larger fish would provide a boon to tourism as more anglers would head for the lake. 

Lake Tahoe straddles the state line between California and Nevada.

©Madhu Gopal/Shutterstock.com

A Huge Oversight Regarding Tiny Shrimp

However, officials failed to consider this shrimp’s hatred of light. Because of the lake’s clarity, the shrimp remain in the deepest parts of the lake during the day. At night, they rise to the surface to feed. But, when the sun rises in the morning, these shrimp dive back down to the darkness of the depths.

The fish of the lake, by and large, are unable to consume the shrimp in great numbers because of this nightly migration, thus defeating the entire purpose for which the shrimp were introduced to the lake in the first place. With little predation to quell their numbers, the population of these invasive shrimp has exploded in the lake.

Fighting Back

Researchers, environmentalists, and residents are fighting back, though. The rallying cry of “Keep Tahoe Blue” has spurred many to take steps to reverse the direction of the lake’s diminishing blue clarity.

Studies and test programs are underway to determine how the mysis shrimp can be removed from the waters in large enough quantities to allow the zooplankton to return and restore a natural balance to the lake’s ecosystem. One of the more interesting initiatives involves harvesting shrimp to make dog treats. Mysis shrimp are rich in Omega-3 fatty acids.

The Water Remains Amazing

Even with the effects of the development around the basin and the introduction of this invasive shrimp species, Lake Tahoe still features some of the purest water in North America. Just how pure is it? Consider this: commercially distilled water is 99.998% pure. The water of Lake Tahoe is 99.994% pure. The tap water in the region that originates from Lake Tahoe is consistently rated as the best-tasting tap water in the nation.

Lake Tahoe has been designated an Outstanding National Resource Water under the federal Clean Water Act. It is still considered the clearest large lake in the world. Thankfully, a committed group of people are dedicated to combatting yesterday’s mistakes to help the lake retain this distinction in the future.

Lake Tahoe Sierra Nevada, California, USA

Lake Tahoe’s clear waters reflect the sky, making for amazing sunsets!

©iStock.com/CelsoDiniz

It’s Up to All of Us

Approximately 15 million people visit Lake Tahoe each year. It is incumbent upon every last one of them to act responsibly to help “Keep Tahoe Blue.” The waters of this alpine lake are a treasure, one worth preserving for future generations.

Mark Twain isn’t the only one who would wax poetic about this lake. In 1873, famed naturalist John Muir wrote, “Tahoe is surely not one but many. As I curve around its heads and bays and look far out on its level sky, fairly tinted and fading in pensive air, I am reminded of all the mountain lakes I ever knew, as if this were a kind of water heaven to which they all had come.”

The photo featured at the top of this post is © topseller/Shutterstock.com


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About the Author

Mike is a writer at A-Z Animals where his primary focus is on geography, agriculture, and marine life. A graduate of Cincinnati Christian University and a resident of Cincinnati, OH, Mike is deeply passionate about the natural world. In his free time, he, his wife, and their two sons love the outdoors, especially camping and exploring US National Parks.

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