Rat Lake Swamp and Popple River Headwaters is important as a nearly roadless area in an extensive wetland complex providing interior forest habitat. A series of black spruce and tamarack, mixed conifer, and northern white cedar swamps is drained by Rat Creek into the Popple River. North of the river, the uplands are generally well-drained and most stands are dominated by pole-sized sugar maple hardwoods. Throughout the site, drumlin tops and well-drained uplands are sugar maple dominated while hemlock and white cedar dominate the foot of drumlins and other poorly drained areas. Rat Lake is a hard-water excellent kettle bog situated in pitted outwash of the Popple River headwaters. The sedge-sphagnum-ericad mat is well-developed and botanically rich. Flora includes numerous ericaceous species, orchids, sedges, and insectivorous plants. Surrounding the wetland swamps are pockets of old-growth hemlock and sugar maple forest containing a large component of super-canopy white pine. The groundlayer is rich, particularly on the drumlin tops, but poorer and dominated by sugar maple seedling in areas of closed canopy. The shrub layer is poorly developed with American fly honeysuckle the most common. The ground layer includes violets, lycopods, wild sarsaparilla, rosy twisted-stalk, northern beech fern, yellow bluebead lily, and mountain wood-sorrel. Richer soils support wild ginger, bloodroot, blue cohosh, and three species of Botrychium. South of Rat Lake, a narrow esker winds through the site. Portions are dominated by sugar maple; others by hemlock and white cedar. Very large stumps are still present among the remaining old-growth trees. Of note are the numerous rare plants present, including a state-endangered species. Rare and uncommon bird fauna includes osprey, yellow-bellied flycatcher, gray jay, wood thrush, veery, Philadelphia vireo, Connecticut warbler, Nashville warbler, and black-throated blue warbler. Rat Lake Swamp and Popple River Headwaters is owned by the U.S. Forest Service and was designated a State Natural Area in 2007. This site is also recognized by the Forest Service as an established Research Natural Area.