Lake Untersee has an unexpected temperature profile in a region known as the anoxic trough. The anomaly is different from observed profiles of other lakes in that, it is smaller in size, occurs at a region known to harbor dense microbial communities supported by extremely high methane concentrations, and relatively deep in the water column. To understand the system, a thermal analysis including a finite difference approach was conducted to define the required energy sources. This was followed by investigation of chemical, biological, and physical inputs to the system to determine a plausible source or combination of sources. The results suggest that solar radiation is the source of energy responsible for heating the water and microbial metabolic reactions do not contribute significantly. However, the microbial populations act as sources of opacity to convert the solar energy into heat. I developed a finite difference mode which enabled us to evaluate potential sources of energy. This work was conducted under the guidance of Dr. Chris McKay at NASA Ames and Dr. Dale Andersen of SETI.