First calendar day of Spring, I think. The lighter blue color toward shore, I'm guessing that's because of depth and turbidity. When the lake is rough, sediment (sand)
is pushed around. When it's calm the shallow depth registers the sandy bed in light blue green/sand hues. When it's rough it mixes and the color is more uniform. I don't know if that's the case, but it can be seen from above too. Satellite images show the same types of hues.