U.S. Water News Online
RENO, Nev. -- Lake Tahoe's clarity last year hovered around
the same range it has been the past five years after showing a marked
decline in previous decades into the late 1990s, researchers said.
The lake's waters were clear to an average depth of 72.4 feet in
2005, a slight change from the average depth of 73.6 feet that a
white plate called a "Secchi disk" could be seen the year before,
scientists at the University of California-Davis said in an annual
When measurements began in 1968, the disk was visible at an
average depth of 102.4 feet. With few exceptions, the clarity level
steadily declined on average through the 1970s into the mid-1980s.
The worst reading was recorded in 1997 -- 64 feet -- the year
then-President Clinton and Vice President Al Gore convened an
environmental summit at the lake to address growing concerns about
pollutants and soil particles in the waters.
U.S. Interior Secretary Dirk Kempthorne and others will reconvene
the summit for an update a restoration efforts at the lake, the
second deepest lake in the United States at 1,645 feet, behind
Oregon's Crater Lake at 1,949 feet.
Scientists believe the fine particles of soil and nutrients that
fuel algae growth are causing the loss of clarity. The pollutants
enter the lake through erosion, runoff and atmospheric deposition.
The clarity is directly affected by the scattering of light by
fine particles and by the absorption of light by algae, the experts
John Reuter, associate director of the UC Davis Tahoe
Environmental Research Center, said the clarity varies from year to
year because precipitation varies. He said that makes it difficult to
use data from any single year or even a small number of years to draw
conclusions about whether the lake is improving overall or getting
He said restoration efforts led by local, state and federal land
managers in the Tahoe Basin are focused on the long term.
"While this year's clarity number is encouraging, the annual
measurements remind us how crucial it is to stay the course in our
efforts to restore Lake Tahoe and to preserve it for future
generations," said Julie Regan, spokeswoman for the Tahoe Regional
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