Why is the Mediterranean Sea so blue?

Clear ocean water absorbs longer wavelengths of light (red, orange, yellow) and scatters shorter wavelengths (blue). In nutrient-rich waters, phytoplankton use chlorophyll, which absorbs blue and red light and reflects green, giving the sea a greenish hue. The Mediterranean is relatively nutrient-poor, especially in summer when a warm surface layer stops nutrients from rising from deeper water. With fewer plankton, the water stays deeply blue. The bright sunshine and pale sandy or rocky seabed along many coasts can also enhance the vivid colour.