Using Water Temperature in Locating Fish

The angler should know how to locate fish by temperature. Probe a lake’s depth with a thermistor on a calibrated cord. The thermistor registers instant temperatures and the cord marks the depth. I have used a Depth-O-Therm instrument for years. There are newer models out which also register oxygen content, pH, and water clarity. These instruments are useful lake fishing tools. With whatever instrument you select, document the temperature at one foot intervals from the lake’s top to its bottom. You rarely need to go deeper than forty feet because it’s rare to find fertile water deeper than this depth. Simply find the depth corresponding to the preferred temperature range of the fish species you are seeking. Then identify the ideal temperature depth which coincides with the lake’s bottom structures that produce both food and cover. This is a likely spot to find actively foraging fish.

Other factors such as light intensity, water clarity, pH, and oxygen content influence the fish by forcing them to migrate where these factors are favorable.

During hot temperatures when the epilimnion layer is unfavorably warm, find the junction of the epilimnion and thermocline. At this juncture the most oxygen and somewhat cooler temperatures will be found. Target this junction at depths corresponding with bottom structures presenting both food and cover. At these times all of the lake’s fish may be concentrated into this narrow zone.

Since a stream’s current thoroughtly mixes its contents, a single thermometer recording at one location will suffice. The closer this temperature is to the fish’s ideal range, the more active the fish will behave. This activity level determines how aggressively fish will feed. For instance, during extreme cold, fish forage in narrow feeding lanes close to their resting lies. On the other hand, ideal temperatures activate fish into chasing food all over the place including the surface film. During ideal temperatures, fish will be attracted to the feeding areas and away from the resting lies. So temperature influences the angler’s fly selection, size, presentation and retrieve.