Clarity depths turn cloudy
Lake Tahoe’s water clarity last year appeared to have reversed the gains in depth reported during the previous two years.
The average depth at which researchers from the UC Davis Tahoe Research Group could see a white disk dropped into the lake in 2000 was 67 feet. The average reading was based on 35 measurements taken during the best viewing conditions.
Although last year’s clarity reading is down from 1999’s 69-foot reading, researchers and environmentalists don’t seem to be alarmed.
“The clarity worsened a little bit,” said UC Davis researcher Bob Richards, “but it’s nothing to get really excited about.”
Richards and The League to Save Lake Tahoe communications director Heidi Hill Drum said the average depth of the lake’s clarity has fluctuated substantially from year to year since the Research Group measured the lake’s clarity at more than 100 feet in 1968.
Tahoe’s famous clarity diminished by 12 feet in one year in 1997, offering only 64 feet of clarity, the worst reading ever.
UC Davis researchers attributed the hefty drop to large amounts of sediment that washed into the lake during flooding in ’97.
“The lake is able to recover from heavy periods of sediment,” Richards said, based on recent and past historical trends.
Because of that, Hill Drum said she’s not too worried about last year’s decline and said people shouldn’t get discouraged when carrying out Best Management Practices on their property.
“(The variable clarity) is typical. You see some ups and downs over the years,” she said. “The things we’re putting into place right now are going to take a long time to see results. It will probably be eight to 10 more years before we can really see the difference.”
Tahoe Regional Planning Agency public affairs coordinator Pam Drum was not as optimistic as Hill Drum about seeing notable results this decade.
“You have to look at the long-term trend that the lake’s clarity is declining,” Drum said. “We have always known that the lake would be slow to react to positive changes in the watershed.”
However, Drum and Hill Drum are optimistic the Environmental Improvement Program projects, BMPs and other restoration and conservation projects will benefit Tahoe’s gem.
“Everybody needs to do their part and if they do we’ll save the lake,” Hill Drum said. “It’s part of the rules for living in this beautiful place.”
The development around Lake Tahoe has been largely to blame for the continued loss of lake clarity, averaging a foot and a half per year. Nitrogen- and phosphorous-rich nutrients from shore erosion, air pollution, untreated stormwater runoff and other factors spur the growth of algae in Lake Tahoe, causing the decline.
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