Similar to light zonation, thermal stratification or thermal zonation is a way of grouping parts of the water body within an aquatic system based on the temperature of different lake layers. The less turbid the water, the more light is able to penetrate, and thus heat is conveyed deeper in the water. Heating declines exponentially with depth in the water column, so the water will be warmest near the surface but progressively cooler as moving downwards. There are three main sections that define thermal stratification in a lake. The epilimnion is closest to the water surface and absorbs long- and shortwave radiation to warm the water surface. During cooler months, wind shear can contribute to cooling of the water surface. The thermocline is an area within the water column where water temperatures rapidly decrease. The bottom layer is the hypolimnion, which tends to have the coldest water because its depth restricts sunlight from reaching it.  In temperate lakes, fall-season cooling of surface water results in turnover of the water column, where the thermocline is disrupted, and the lake temperature profile becomes more uniform.
Boris is deploying a camera probe in a lake to observe the different kinds of fish species that reside in each layer during the summer. In order to make sure he is at the right depth and thus in a different layer each time he makes observations, he needs to measure the water temperature. The temperature for Measurement A reads 75 degrees Fahrenheit. The temperature for Measurement B reads 55 degrees Fahrenheit. The temperature for Measurement C reads 40 degrees Fahrenheit.
Is Measurement A or Measurement C most likely the hypolimnion?