Thermal Break - Randomly occurring surface temperature gradients. The break gradients may range from 3-10 degrees Fahrenheit over a relatively short trolling distance. These breaks tend to be the most productive fishing areas at the sharpest breaks. This transition is a period of time where the frozen or near freezing surface waters, with underlying warmer waters, change to a body of water having warmer surface water temperatures underlaid by cooler water temperatures. The Great Lakes warming processes and features vary slightly in degree and timing due to the differences in the lakes' water volume and regional climate.
Temperature is less of a fish-catching factor as summer becomes fall.
This is because fish enter river mouths and many move upstream.