According to a recent article in the Tahoe Regional Planning Agency’s Tahoe in Depth Newsletter, the clarity levels of Lake Tahoe are improving. Lake clarity increased due to several factors, high among them being the continuing drought. Lower amounts of precipitation means less runoff into the lake, which means that fewer pollutants find their way into Tahoe’s waters. The extreme regional drought has brought a small glimmer of good news, but that news pales in comparison to its terrible effects elsewhere. However, if we focus on the bright side, Lake Tahoe clarity levels are at a decade long high.
Water clarity in Lake Tahoe is measured using a Secchi Disk. The Secchi disk is a white disk that is lowered into a body of water. The clarity measurement is then obtained by seeing how far the Secchi disk can lowered into the water while still remaining visible. In Lake Tahoe, the clarity has historically been remarkable, with data suggesting clearness to approximately 120 feet. While the lake is nowhere near that clear now, currently hovering around 70 feet, it is still a measure of how the lake is currently faring in its ever-expanding use.
Water clarity is an important indicator of lake health. One of the reasons for Lake Tahoe’s remarkable clarity is due to the amount of rain that falls directly on the lake. Approximately 40% of rainfall that contributes to the lakes watershed is directly onto the lake itself. This is a very large amount of water that does not have to flow into the lake via runoff, meaning that the clarity is not negatively impacted.
Several measures have been taken to increase Lake Tahoe’s clarity levels, including the very popular “Keep Tahoe Blue” campaign (more information can be found here). Another important tactic is the institution of the Lake Tahoe Total Maximum Daily Load, which WETLAB has previously written about here.