title: Google Maps coloured overlay/polygon that only applies to water
body: <p>I need to plot some coastal areas that are are easily defined in English (eg "water in the bay north of latitude X"), but are highly complex polygons because of the shoreline.</p>
  
  <p>Do I have to plot the the entire (relevant) section of shoreline, or is there a way to draw a rectangle that only colours the water (and has no effect on land)?</p>