Why is Tahoe so clear?

One reason Lake Tahoe is so clear is that 40 percent of the precipitation falling onto the Lake’s watershed falls directly upon the Lake. The remaining precipitation drains through marshes and meadows, which are a good filtering system for water. Unfortunately, many of the Lake's natural filtering systems have been disturbed by development and Tahoe's clarity is diminishing. Scientific measurements of water clarity started in 1968. At that point, one could see a white disk submerged to a depth of 100 feet. Today, clarity has dropped to around 60 feet. That means Tahoe is losing about one foot of clarity per year.