Crystal Lake is located within the Northern Highland-American Legion State Forest, Vilas County.
It is a seepage lake with predominantly sand substrate. It has a surface area of 36.7 hectare, 2.3 kilometers of mostly undeveloped (campground) developed shoreline and a maximum depth of 20.4 meters.
Crystal Lake represents one extreme in the groundwater input gradient, with a marked predominance of precipitation inputs. Groundwater accounts for only 5% of input water, yet, because groundwater is more concentrated chemically than precipitation, groundwater accounts for substantial amounts of incoming solutes. For example, about 50% of the silica budget comes into the lake via groundwater, exerting a major influence on primary production.
The lake is an oligotrophic, dimictic lake high in the landscape with minimal groundwater input, a light attenuation coefficient of 0.24 per meter (average ice-free Secchi depth of 8 m), a mean depth of 11.4 m, and a maximum depth of 20.4 m. Crystal Lake is circular with a shoreline development factor very close to 1.0. The littoral zone is fairly homogenous and is dominated by sandy substrate with low macrophyte and coarse woody habitat densities. The fish community has been historically dominated by pelagic yellow perch. However, yellow perch drastically declined after the detection of rainbow smelt in 1985.