“Light bottomed flats reflect a large portion of the sunlight. When water temperatures are at the extreme end of the comfort zone of saltwater fish, generally during the months of July, August and September, fish will often prefer to frequent light bottomed or sandy coral flats because the water temperatures will be a little cooler.” That’s Kent Klewein of Gink & Gasoline summarizing the effect of light bottoms on water temperature.
What he says is true, and anyone who’s fished the dark-bottomed Everglades or deep grassy flats for wintertime permit will also intuitively understand the opposite effect: dark bottoms draw fish in cooler weather. But tides and solar heating play an equally important role. Incoming water fresh from the depths of a channel can be warmer than the flat it covers in very cold weather, and water than has been sitting in a sunny basin for hours before ebbing out in the late afternoon can be the warmest you’ll find all day.
As fish feel the first touches of fall, keep in mind that the newly cool water will pull fish up onto the flats for several weeks. But when that first big cold front hits, you’ll want to shift your strategy to looking for the warmest spots and the flats least touched by the change in wind direction: those in a wind shadow or with deeper areas adjacent to drop-offs.