Scientists track Tahoe clarity loss |

Scientists track Tahoe clarity loss

Gregory Crofton
Dan Thrift / Tahoe Daily Tribune / The clarity of Lake Tahoe declines by nearly 12 inches a year.

Chipping away at the difficult task of pinpointing why Lake Tahoe’s clear water is fading at the rate of a little less than a foot per year, scientists met at Stateline last week to discuss what they’ve figured out thus far.

“We realize the fine particles are an important part of what’s happening here,” Geoffrey Schladow told more than 100 scientists and restoration specialists who gathered for a two-day symposium at Embassy Suites Hotel.

“Most of the particles that enter the lake are tiny – a micron – individually you can’t see them,” Schladow said. “This was the elephant in the room as far as we can see.”

Until concerted scientific research effort began two years ago to figure out exactly what is going into the lake and where it is coming from, the general theory was that algae growth fueled by nitrogen and phosphorous was the primary cause of clarity loss.

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Now data indicates that fine particulate matter, which disperses sunlight as it tries to make its way down into the lake, constitutes about 50 percent of the problem.

“Light scattered by fine particles is sometime as high as 70 percent, other times 40 to 50 percent (of the problem),” Schladow said.

The collective work of all of the scientists will be put into a clarity model that Schladow has created and be used to formulate the amount of fine particles of sediment, nitrogen and phosphorous the lake can absorb without continuing to lose clarity.

Those numbers – called the Total Maximum Daily Load – will be incorporated into Pathway 2007, a planning effort under way to create 20-year resource and land management plans for the Lake Tahoe Basin.

“We’re really making progress toward solving Tahoe’s problem at a rate we haven’t seen at previous times,” said Charles Goldman, who founded the UC Davis Tahoe Research Group in 1959. “We’ve got the talent, and with luck, we may even have enough money to accomplish the job. Most important is that the scientific brain power is being assembled in the Tahoe basin to really meet the difficult complex problems.”

Today Tahoe’s average clarity depth is 66 feet. The goal is to stop clarity loss and restore it to 97 feet. Figuring out ways to stop the bleeding by limiting the amount of fine particles of sediment and how much nitrogen and phosphorous ends up in the lake is part of the Total Maximum Daily Load scientific effort.

It involves the creation of a “toolbox” to help identify crucial environmental restoration projects and create regulations that allow the public and its agencies to limit negative impacts on the lake.

Since Tahoe became a popular place to live and for people with cars to visit, the basin has lost 75 percent of its marshes, 50 percent of its meadows and 35 percent of its stream-zone habitat, according to the Tahoe Research Group. All those natural features helped protect the lake by trapping sediments and nutrients on land.

– Gregory Crofton can be reached at (530) 542-8045 or by e-mail at

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