The degradation of Lake Tahoe s clarity is a topic of concern and study, particularly in the near-shore environment where changes in clarity are most apparent to residents and visitors to the region. The Tahoe Research Group has made measurements of clarity in the deepwater portions of Lake Tahoe since the 1960s.
Results indicate that clarity is decreasing with time.
A related optical property is turbidity, which is a measure of how light is scattered by particles in the water. Turbidity can be measured continuously so that short duration changes in the optical properties of the water can be detected. Sampling periods are designed to capture seasonal variations in turbidity prior to, during, and after peak runoff. However, because turbidity in the littoral zone can vary strongly in both space and time, there is concern that the discrete sampling program may not properly capture both the temporal and spatial variability and therefore may not provide the optimal data needed for monitoring and detection of long-term change. While standard calibrations of the intake turbidity instruments are performed on a regular basis by the water purveyors as required by the Safe Drinking Water Act , the suitability of the water intake data for detection of long-term changes in lake turbidity and monitoring is not clear.