Crystal Bog (27-2) is located within the Northern Highland-American Legion State Forest, Vilas County.

It is a small and shallow bog lake. It has a surface area of 0.5 hectare, mostly undeveloped shoreline and a maximum depth of 2.5 meters.

Bog lakes are isolated to a large extent from surrounding groundwater flow systems. However, they exhibit a similar pattern, across landscapes, to that exhibited by other lakes in general. The proportional input of groundwater to the bogs' hydrologic inputs increases with decreasing elevation in the landscape. More detailed studies of Crystal Bog reveal a complex interplay between conditions in the lake and in the surrounding wetland due to the groundwater flow regime and resulting chemical transfers.