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True-Blue Science to Save Lake Tahoe

When Geoff Schladow was a child, Booker T. and the M.G.’s were on the radio playing “Green Onions,” and the waters of Lake Tahoe were intensely, absurdly blue. You could drop a white disc into the water and watch it, with your naked eye, sink more than 100 feet below the surface.  

Fast forward to today. Schladow, now director of the Tahoe Environmental Research Center at UC Davis, was recently watching Booker T. play to a crowd at Sand Harbor on Tahoe’s east shore. The music — and the scientist that he is — led Schladow to think about the changes the lake has seen in the years since 1962 when “Green Onions” started walking its haunting bass line for the first time.

A lot has happened in that time: Development has encroached around the lake. Species like milfoil, Mysis shrimp and Asian clams have invaded its shoreline and waters.  Summers have gotten hotter and longer. The snowpack has shrunk. Wildfires have raged.  And lake clarity has decreased from more than 100 feet in the 1960s to an average of 78 feet today.

One thing that’s been consistent for all of that time is UC Davis’ close eye on Lake Tahoe. University of California Professor John LeConte took the first scientific measurements in Lake Tahoe in 1868 — just a few years before Mark Twain would famously describe the lake as “surely the fairest picture the whole world affords.”

University of California Professor John LeConte took the first scientific measurements in Lake Tahoe in 1868 — just a few years before Mark Twain would famously describe the lake as “surely the fairest picture the whole world affords.’

Then in 1958, UC Davis limnologist Charles Goldman began conducting research at Lake Tahoe, pioneering more than 50 years of consistent data on the lake environment — a legacy Schladow and TERC scientists continue today, often in partnership with agencies and researchers across the region.

Secchi disc measurements

Every 10 days since 1968, UC Davis scientists have lowered the white Secchi disc into Lake Tahoe to record its clarity, which is regarded as the key indicator of its overall health.

By 1997, Lake Tahoe was in a crisis. Lake clarity had dropped nearly in half — from 102 feet in 1968 to 64 feet. President Bill Clinton and Vice President Al Gore convened the first Tahoe Summit that year, ushering in an era of bi-state, bipartisan support to save the lake, which straddles California and Nevada.

The summit set the stage for passage of the first Lake Tahoe Restoration Act, which allotted federal and private funds to preserve and restore the lake. Since then, $1.74 billion in public and private funding has been invested to improve the lake’s environment.

Tahoe is worth saving

While efforts to preserve the lake have not been free from all political tensions, federal and state leaders from both states agree that one of the nation’s biggest and bluest lakes is worth saving. They have met for each of the past 18 years at the Lake Tahoe Summit to publicly renew that commitment.

Last year’s Aug. 18 summit in South Lake Tahoe brought together California and Nevada elected officials.

On the California side were Sen. Dianne Feinstein, Gov. Jerry Brown, Rep. John Garamendi and Lt. Gov. Gavin Newsom. From Nevada came Sens. Harry Reid and Dean Heller, Gov. Brian Sandoval and Reps. Tom McClintock and Mark Amodei.

What’s trying to damage the lake

“Drought, wildfire, invasive species — they are ruining this country, and they are really trying to damage this lake,” Reid said.

Providing the scientific foundation that federal, state and local government agencies use to assess the lake’s health and guide management decisions is the annual Tahoe: State of the Lake report, prepared since 2007 by the UC Davis Tahoe Environmental Research Center and released just a few days before the summit.

“Without an unassailable data record, we would not be discussing how best to restore Lake Tahoe,” Schladow told the crowd at the summit. “We would be arguing about whether it had changed at all.”

Not so simple

This year’s data showed that lake clarity has been stabilizing and has improved since the 1997 summit from 64 feet to 78 feet.  It also showed the impact of climate change and drought: The lake level rose by only 11 inches during the spring snowmelt, which is far below normal. Lake Tahoe fell below the natural rim on Oct., 16 2014, stopping its outflow to the Truckee River.

“It used to be simple at Lake Tahoe,” Schladow said. “It was all about controlling development and the pollution that came with it. That’s no longer the case; it was probably never the case.

“We now recognize that while development was taking place, other factors were changing simultaneously — the climate, new species, increasing biomass in the basin and the impacts of the increasing number of wildfires outside the Tahoe Basin."

New tools and models help measure

‘While it may be convenient to separate the issues — clarity, invasive species, drought, ecosystem health, climate change — they are not separable.’

— Geoffrey Schladow

And it’s not all about the white disc anymore. A variety of computer models, sensors and other equipment is being used to measure everything from how water moves and mixes, to water chemistry, nutrient levels, oxygen, temperature and how all of that influences the introduction of more visible indicators, like invasive species, algae, lower lake levels and wildfire.

For example, last August, TERC initiated a network of sensors to monitor the nearshore environment, where most people experience the lake. The sensors will provide real-time data about water quality along the nearshore, collecting information agencies can use to explore solutions to improve this area of the lake.

Research extends to other ecosystems

TERC scientists have taken the lessons of Lake Tahoe to help lakes worldwide struggling with similar challenges. For instance, managers of New York’s Lake George sought TERC’s advice for its invasive Asian clam problem. (An Asian clam control project in Tahoe’s Emerald Bay killed 90 percent of the clams there, TERC reported this year.)

The researchers are also working with researchers in New Zealand to understand how sediments enter lakes and they are advising lakes and fisheries experts in Bhutan.

Providing meaningful advice

“While it may be convenient to separate the issues — clarity, invasive species, drought, ecosystem health, climate change — they are not separable,” Schladow said.

“They all interact, and we can only provide meaningful advice if we understand them and think about the Tahoe Basin as an interconnected system.”

TERC also takes its education and outreach mission seriously. They teach the public about freshwater ecosystems at TERC’s two public education centers, one in Incline Village at the Sierra Nevada College campus and the other housed in a historic fish hatchery in South Lake Tahoe.

About 12,000 people visit the centers each year to watch 3-D movies of Lake Tahoe, play with a high-tech “sandbox” that teaches about watersheds in a truly hands-on way, climb aboard a virtual research vessel, hear educational talks on a variety of Tahoe topics, and learn more about the Tahoe Basin.


Editor's note: Each year UC Davis researchers deliver a “State of the Lake” report for Lake Tahoe. This story about UC Davis’ long involvement with the lake was first published in August 2014 and has updated figures from 2015.

Media contact(s)

Gregory Urquiaga