Lake Tahoe clarity improves but climate change takes toll, report says

The news is mixed for Lake Tahoe: Drier years and less precipitation mean less runoff and improved water clarity, but that same long-term warming trend will drive up water temperatures and lower water levels.

Those are among the conclusions found in a report “Tahoe: State of the Lake Report 2013,” released Wednesday by the Tahoe Environmental Research Center at UC Davis.

Clarity of the lake improved in 2012 for the second straight year, to 75.3 feet, an improvement of 6.4 feet. The target to maintain Lake Tahoe’s iconic clear blue waters is 78 feet.

Researchers noted that with precipitation in 2012 only 71% of average, fewer pollutants flowed into the lake. In addition, the report found an absence of wintertime “deep mixing,” when cool surface waters sink, bringing nutrients to the surface.

The action promotes algae growth, which clouds waters, but also warmer lake temperatures. Last year the annual average surface temperature of the lake was nearly 53 degrees, the highest ever recorded.

UC Davis has been monitoring Lake Tahoe since 1968 and the long-term climate trends indicate a net loss in water level, rising by 1.3 feet during snow melt, compared with 3.9 feet the year before and falling during dry months by 2.3 feet.

@julie_cart