Fremont Lake was formed by glacial scouring and blocked at the outlet by a terminal moraine. The lake lies at an altitude of 2,260 m, having a volume of 1.69 km3 and an area of 20.6 km2. Fremont Lake is elongated, having a length of 8.14 km, a width of 1.57-2.08 km, and a maximum depth and mean depth of 185 m and of 82 m respectively. As would be expected from the lake chemistry, the watershed is also reasonably pristine. The 196 km2 drainage basin originates from the western slope of the continental divide and is largely comprised of the Bridger Teton National Forest Wilderness Area.
Pine Creek enters the northern end of the lake and serves as the only significant tributary.
Water quality problems originating for the drainage basin are not expected to be significant. The Surface Water Treatment Rule and Filtration Avoidance Criteria Requirements. Furthermore, the SWTR specifies a multiple protection barrier using filtration and disinfection as the best treatment techniques, as an alternative to establishing maximum contaminant levels for these microorganisms. In 1991 the SWTR went into effect, and the town of Pinedale was notified that it must comply with the rule. However, the town made a decision not to provide any treatment to their drinking water beyond chlorination.