Lake Tahoe, the jewel of the Sierra once so crystal-clear that Mark Twain likened boating on it to floating on air, is warmer and soupier than ever before as a result of climate change and human activities, UC Davis scientists reported Wednesday. Their report, Tahoe: State of the Lake 2007(PDF 45 pages), the most comprehensive ever done on the lake, outlines significant changes in weather patterns over the years, including less snowfall and more rain, deteriorating lake clarity and increasing water temperature in the Lake Tahoe Basin - all of which could increase invasions of exotic fish and plant species... The most significant finding... is how much the Tahoe climate is warming. Low temperatures at night have risen 4 degrees on average, and the number of days with temperatures that averaged below freezing dropped from 79 days to 52 days since 1910. The percentage of precipitation that falls as snow has also decreased, from 52 percent to 34 percent in the 96 years studied. All of this is apparently having a major effect on the lake. The average temperature of the surface water in July has increased almost 5 degrees, from 62.9 degrees to 67.8 degrees since 1999, according to the report... The water temperature was 78 degrees on July 26, 2006, the warmest in Lake Tahoe's recorded history. Clarity also has suffered. In 2006, Lake Tahoe was clear to an average depth of 67.7 feet.. When measurements began in 1968, the lake was clear to an average depth of 102.4 feet.

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