There are two methods of measuring the clarity of the lake. One is using a secchi disc, a round, flat white plate, lowered into the water until the human eye can no longer see it. A pulley on the boat measures how far the disc has gone down until it can no longer be seen and this determines clarity levels. Another method used is an underwater submarine with a photo cell which detects light. This allows someone to compare the surface sunlight with the different depths.
Erosion is just one of many factors contributing to a decrease in the lake's clarity.
Phosphorous and nitrogen are known causes of algae growth. Anything from automobiles to fertilizers to watercraft can put nitrogen and phosphorous in the water, Hill said. Even air pollution coming from neighboring cities such as San Francisco and Sacramento can contribute to the decrease in the lake's clarity, Richards said. However, it is still unknown how much any of these factors contribute to the nutrient growth, Richards said. The primary source of phosphorous growth is land sources, Hill said.