This is the exact same way you would normally find the darkest parts of the image when you're removing any color casts from the shadow areas, but now, thanks to the Difference blend mode, these darkest areas represent the areas closest to midtone gray.
The warmest sea in Key Largo in March is 26Â°C/79Â°F, and the coldest sea temperature in March is 22Â°C/72Â°F. Average water temperature in Key Largo in March is 24Â°C/75Â°F. You can choose any other years:
In Key Largo, Florida Keys in the month of April the Ocean water temperature averages between 80F at a high and 76F at a low from my experience. Many times in April when you are diving in Key Largo, you will swim through warm pockets of water.