This week, a historically dry period in California will come to bear at Lake Tahoe, where the water level is expected to sink below the basin’s natural rim. That’s the point at which the lake pours into its only outflow, the Truckee River.
It’s not a crisis, researchers and conservationists say, but it marks another extreme swing for Tahoe amid historic drought, wildfires and erratic weather, all intertwined with climate change and becoming more prominent aspects of the alpine environment.
“Going below the natural rim won’t change much in the lake itself. But there’s very little positive about low lake levels once they get below the rim,” said Geoffrey Schladow, director of the Tahoe Environmental Research Center at UC Davis.
Tahoe’s natural rim rests at 6,223 feet in elevation. A dam on the Truckee River allows the lake to fill about 6 feet higher, to 6,229.1 feet, according to the U.S. Geological Survey.
The water level has fallen below the rim four times since 2004, most recently in the fall of 2016, the height of California’s historic drought. However, that tense period was followed by a banner winter for precipitation in the Tahoe area, in 2017, which replenished the Sierra snowpack and brought the lake to its highest heights in decades.
The water level has mostly been falling since the summer of 2019, when it was near the lake’s limit, and is currently about 1½ inches above the rim. The plunge is due primarily to meager snowpack in the mountains ringing the lake as well as evaporation, which sucks about 3 feet of depth off the lake each year, according to Tahoe water authorities.
This time, researchers and environmental nonprofits keeping watch of the lake aren’t optimistic about the water coming back as quickly as it did in 2017.
“If we have another dry winter, it could become a bigger concern,” Schladow said.
Tahoe has been steadily receding all year, and the plunging water level is changing the character of its shoreline.
The Truckee River, Tahoe’s only outflow, has slowed to a trickle. Private piers across the North Shore are high and dry. Boat ramps plunge straight into bare earth. Entire coves on the East Shore, popular with kayakers, have dried up. The South Shore has become one giant sandbar. Beaches in shallower areas have grown by hundreds of feet, exposing parts of the lake people aren’t used to seeing and revealing stinking deposits of rotting algae.
“You can’t get within 150 yards of the normal shoreline” in South Lake Tahoe, said Kelsey Weist, owner of Clearly Tahoe, which runs clear-bottom kayak tours around the lake.
The brunt of the impact so far has been felt by boating and tourism companies who have had to get creative about getting their customers on the water. Marinas are dredging more deeply to retain access for boaters.
Weist, who runs tours year-round, has adapted by overhauling her routes. A popular one that led paddlers along the Upper Truckee Marsh — typically a great place to spot wildlife — had to be canceled in early July, Weist said.
“We don’t foresee this being the last time we have this challenge,” Weist said. “With global warming, we know we’re never going to be able to anticipate a normal season again.”
The lakebed is exposed at Kings Beach on Sunday — the water level is so low at Lake Tahoe that it in danger of becoming stagnant.
Max Whittaker/San Francisco ChronicleUpper Truckee Marsh marks the spot where Tahoe’s largest inflow, the Upper Truckee, reaches the lake. It’s key habitat for kokanee salmon, which would normally be running upriver this time of year by the hundreds to spawn. But on Friday, under the afternoon sun, Jesse Patterson looked into the water there and counted only two. Nearby, piles of dead algae decayed on the beach.
“It’s crazy low,” said Patterson, chief strategy officer for the League to Save Lake Tahoe, a conservation and cleanup nonprofit. “The concern is what it looks like if this continues for multiple years in a row.”
Beyond cosmetics, there’s potential for environmental effects.
Climate change has warmed the lake, which has in turn given rise to algal blooms that have, in recent years, mucked up its famous clarity. The warmer the lake gets, the less likely it is to “turn over,” a periodic mixing phenomenon that helps keep the aquatic ecosystem balanced and healthy.
If water levels were to remain below the rim, Tahoe could become “terminal,” a designation of water bodies with no outflow. Those lakes come to be known for their high salinity and lack of aquatic life — the Salton Sea and Mono Lake are two examples in California.
Another possible change to Tahoe if water levels remain low: the emergence of the shallow sill at the mouth of Emerald Bay, which could separate the bay from the rest of the lake. Such separation “may occur at the mouths of many streams, cutting off access to spawning kokanee salmon next fall,” according to an email update from the Tahoe Environmental Research Center at UC Davis.
But there is reason for optimism: Snow has already fallen in Tahoe at least twice this month; a quarter-inch fell in parts of the lake on Monday.
“It is likely that winter will arrive in the next few months and the lake level will rise above the natural rim soon after,” according to the Tahoe Environmental Research Center. However, in its email, the center said that things could get worse.
“There is no limit to how many years drought conditions may persist and how low the water level may go. The most recent estimates suggest continuing drought conditions.”
What concerns lake advocates is the overall toll of more frequent extreme events — historic drought and low snowpack, high temperatures, smoky skies, the Caldor Fire.
“It makes us question, is the lake at a tipping point?” said Darcie Goodman Collins, CEO of the League to Save Lake Tahoe. “There’s a lot we can do to help the lake be resilient to climate change — restoring the natural wetlands and streams, invasive species removal. But it’s valid to ask those questions because this is happening so quickly.”
Gregory Thomas is the Chronicle’s editor of lifestyle & outdoors. Email: gthomas@sfchronicle.com Twitter: @GregRThomas
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Lake Tahoe has fallen to an alarmingly low level. Here's what the impact could be - San Francisco Chronicle
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