Lake Tahoe is famous for water so clear, you can see 70 feet below the surface — but have you ever thought about what the lake bed looks like? Few have explored much farther beneath the frigid waves of the nearly 1,600-foot-deep lake, but thanks to a first-of-its-kind livestream from nonprofit the Tahoe Fund and the Restoring the Lake Depths Foundation, everyone can now catch a glimpse of the very bottom.
On Sept. 5, a remotely operated vehicle, or ROV, dubbed Deep Emerald traveled to the floor of Lake Tahoe, which is the second-deepest lake in the U.S., after Oregon’s Crater Lake. Describing Deep Emerald as “built for advanced underwater exploration,” Lindsay Kopf, founder and executive director of the Restoring the Lake Depths Foundation, pointed out in a news release that the vehicle’s 600-meter fiber optic tether makes it the “rare ROV capable of reaching the depths of Lake Tahoe’s deepest points.”
Tahoe Fund
In a livestream that began that day at 9:30 a.m. local time, Tahoe Fund CEO Amy Berry hosted conversations with experts on board the boat that were displayed on one half of a splitscreen. The other half showed the ROV’s journey. Before the vehicle was released into the water, Kopf noted that it’s “equipped with eight thrusters, four LED lights, [and] a 4K ultra-HD camera with low light sensitivity, which makes her a perfect vehicle to be able to see the pitch black abyss at the bottom of the lake.”
Sudeep Chandra, professor of limnology at the University of Nevada, Reno, joined in to shed some light on what might be lurking in that dark abyss. He explained that between 120 to 700 feet below the surface, sub-ecosystems “just like in the oceans” exist, complete with deep water plant beds that are home to 10 animal species only found in Tahoe — including the Lake Tahoe benthic stonefly and two types of blind amphipods.
So what did the team see at the bottom of the lake? The ROV displayed a plethora of flaky sediment materials floating past its lens, including granitic rock. “The lakes are bottom reservoirs of history,” Chandra commented. “Some of that material is present-day, but you could core through the bottom and we could get back to a thousand years ago. Or 2 million years ago.”
He explained that the materials from Tahoe’s watershed get deposited on the bottom of the lake and are then “processed” and returned when the water mixes every four to seven years. For those of us who aren’t limnologists, lake mixing is when water from the top and bottom essentially switch places, dispersing nutrients and replenishing oxygen throughout.
And at the bottom, “the water is blue,” Chandra said, adding, “If you shine light through it, it’s got this hue of blue that’s equally unique as the surface.” He credited the color partially to the small watershed-to-lake ratio, which means that the lake isn’t overly full of materials that would dull its vibrant cobalt shade.
One object that turned up during a prior mission to Tahoe’s depths, but didn’t make an appearance this time around, was a piece of party decor: Kopf recounted that at 1,581 feet below the surface, her team found a perfectly intact “happy birthday” balloon, which she said was “very eerie.” While Deep Emerald has a gripper tool to pick up litter in the lake, the device can’t snatch objects at that great a depth. “So we did have to leave it,” Kopf said, “but we marked it and we’ll be back for it.”
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