Comparing the 1984 (high water level) and 2005 (low water level) images, there is a pale outline along many parts of the lake. When the water level drops, canyon walls that were once inundated are exposed again.
Referred to as the “bathtub ring,” this pale outline shows when the lake is below capacity. Calcium carbonate and other mineral compounds, many of them various salts in the water, attach themselves to the sandstone and leave behind this white mark. The top of the white mark is the high water mark. The only time the bathtub ring is not visible is when the lake is completely full.