Lighter material drops out later. We also have a current running from the bottom of the image to the top right corner. We're focusing on how the coastline is constantly being changed. Lighter, aqua blue, is likely to be shallow. We think they are areas of mud which have dried out and as the H2O evaporated left behind salt.
Salt makes the white colors.
The water isn't polluted, the transported material makes the water look cloudy. Longshore currents cause material to drift down-current. We see an island surrounded by water. We can see different colors and shapes in the water. Think about currents, depths, and material.