It’s a simple test with profound implications. You board a boat, head out to a predetermined location on Lake Tahoe, tie a white disc to a line and lower it into the waters. And down it goes. And goes. When you can no longer make out the white disc, the test is over. You reel it in and measure how far it descended while maintaining a visual on it. Rocket science it most certainly is not. But significant it most definitely is.
The study is called the Secchi Test and has been conducted annually by the University of California Davis’ Tahoe Environmental Research Center for the past 50 years. This spring, when the disc was pulled from the waters, the test revealed a clarity in Lake Tahoe’s waters that hasn’t been present since the 1980s. The annual average clarity at the lake in 2023 was nearly 72 feet, a significant improvement over Tahoe’s second-worst reading of 61 feet measured in 2021.
The explanation behind this big bump in clarity is attributable mainly to zooplankton that eat clouding particles in the water. Prior to this year, numbers of Daphnia and Bosmina zooplankton had been plummeting. Their resurgence provides scientists with hope that they can play a big role in returning clarity to levels last seen in the 1970s and eventually to its historic levels of 97 feet.
Scientists emphasize there’s a lot of work before them to help secure the health of the lake’s legendary waters. As for what you can do? Well, that’s a far easier task: the next time you crest Brockway Summit and catch a glimpse of that big stretch of blue, take a moment to savor its beauty and appreciate the significant role this lake plays in our lives.
written by Scott Mortimore
photo courtesy of Paul Hamill Photography