Just wanted to clarify, the water level is dictated mostly by two things; level of precipitation in the near past and hence the runoff that year into the basin, and the amount of water diverted from the basin for destinations on the western slope of the Sierra.
You can see they yearly cycle of water depth based on the runoff. It shows up as the small 'sawtooth' shapes on the curve. But the majority of the swing is due to the amount of diversion.
