During my recent road trip with my folks to the Big Sur area I was plagued by the question: "Why is the water so blue along the central California coast whereas on the northern California coast the water often appears to be gray or brown?"
The short answer: calmer water that doesn't stir up a lot of sediment + low phytoplankton + low chlorophyll = very clear, thus very blue water.
Vista point south of Carmel
This is the Carmel River State Beach.