If it’s winter where you are, you’d probably rather be here. Cuba, Miami, and the Bahamas frame this blue-green corner of paradise on the edge of the Caribbean Sea. So if water is actually clear, why all the different shades of blue?
Water molecules absorb the red, yellow, and green wavelengths contained in sunlight quite effectively, leaving behind mostly just the blue. Deep, relatively clean water scatters almost nothing but blue light, and so appears as a darker blue. In shallower waters, like around the islands of the Caribbean, reflections off of reefs and sandy bottoms will bring out the yellows and greens. Other factors that affect the local color of ocean waters include algae blooms and particles suspended in river runoff, which all absorb and scatter their own specific wavelengths of light.
Astronaut Reid Wiseman captured this image through the Cupola Window aboard the International Space Station on July 15, 2014.