Tahoe's clarity improves, but temperatures rise
Listen to the story
Clarity is up at Lake Tahoe, but so is average temperature due to global warming. Those were some of the main points raised in the "State of the Lake" report released by The University of California, Davis on Wednesday.
It's the second straight year lake clarity has improved, increasing by more than 6 feet from last year. The lake has lost a quarter of its clarity since researchers first began measuring in 1968. At that time, they could see more than a hundred feet below the surface.
Geoff Schladow is the director of the Davis Tahoe Environmental Research Center. He says while this year is a substantial improvement, it's the long term trends that really matter.
"In my mind anyway, it goes to the point that we are actually capable of very large fluctuations from year to year."
2012 was a dry year. That meant less precipitation and in turn less storm water and pollutants entering the lake. Schladow says it's difficult to say just how much restoration efforts contributed to the increase in clarity because they're not monitored very well.
"But the end goal, as far as we're concerned, is that we'd like to stop pollutants from entering the lake, regardless of weather conditions."
Another key finding was a decline in the presence of a small kind of algae that actually stops light from entering the lake. Schaldow says it's not an invasive algae, but starting about 5 years ago its population exploded and that correlates with the loss of clarity. One explanation is when there's less mixing of different layers of water, the larger types of algae sink to the bottom out of the zone of light.
"By contrast, these very tiny algae, which sink very slowly, suddenly are left up there in the light with no competition for nutrients, so they can grow very rapidly."
At the same time, the report cautions that historically there are years of apparent improvement, only to be overtaken by overall decline in certain conditions. Climate change continues to affect snow melt and the amount of water in the lake. The annual average surface temperature was the highest ever recorded for Tahoe.