To what extent do you suppose water temperature influences fish to bite or not? The fish weren’t biting on anything I tried, so I checked the temperature of water layers.

American Lake is a fairly “stagnant” lake with little water flow-through. It’s temperature layers cycle seasonally. A Fish Hawk Depth/Temperature gauge lowered to the depths records temperatures at 5-foot intervals.

(The NFR "Preview" pane does not permit separate columns, and just pushes the three columns together: depth, January temperatures, and July temperatures.)

January 6, 2016 July 19, 2016

00 45.8 73.9
05 45.5 73.3
10 45.2 72.8
15 45.2 72.5
20 45.2 72.0
25 45.0 70.0
30 45.0 63.3
35 45.0 56.6
40 45.0 54.3
45 45.0 53.1
50 45.0 52.5

“Stagnant” lakes that are deep enough, including American, develop a thermocline in the summer. A thermocline is a narrow layer of water in which the temperature changes rapidly.

Mixing of the water column in the summer doesn't happen because the lighter weight warm water always floats above the more dense cooler water.

Limnologists are scientists who study fresh water lakes. They indicate that the thermocline typically develops around the depth where the energy from the sun becomes very weak. In American Lake, the thermocline develops at about the same depth where rooted vegetation appears to quit growing.

Fish Hawk measurements over a few years show that as summer changes to winter, water temperatures cool from the top down. Likewise, as winter changes to summer, the temperatures increase from the top down.

Fresh water is most dense (heavy) at about 39 degrees F, and expands and becomes lighter as it’s temperature decreases below 39. With one exception, deeper water is always colder than (or the same as) near-surface water. That exception is when the surface layer is cooler than 39F, causing that colder water to expand and “float” on top of the warmer water below.

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