Bark Bay Slough consists of a coastal barrier spit, lagoon, springs, and wetlands occuping an embayment between two rocky headlands along Lake Superior. The wetlands are extensive and include two major types: coastal fen and coastal bog. The fen dominants are woolly sedge, twig rush, sweet gale, water horsetail and buckbean . The coastal bog is composed of a mat of Sphagnum mosses, ericaceous shrubs, sedges, carnivorous plants and scattered small tamarack. Both communities are floristically diverse, in excellent condition, and support many rare species, including Michaux's sedge (Carex michauxiana), downy willow-herb (Epilobium strictum), and dragon's-mouth orchid (Arethusa bulbosa). Two rare butterflies, bog copper (Lycaena epixanthe) and bog fritillary (Boloria eunomia), also inhabit the wetlands. A forested interior sand spit parallel to the coastal barrier spit (or 'bay-mouth bar') breaks the wetlands into two major sections. The sandy, 2-mile long barrier spit contains red pine and white pine with an understory of blueberry, bearberry, alder, sweet gale, and beach grasses. A large lagoon occupies the center of the site and supports submergent and floating-leaved aquatic plants. Together, the wetlands and 28-acre lagoon form a bay-mouth bar lake. The shallow (8 foot maximum depth), hardwater lake supports mostly panfish and northern pike. The Bark River, and a spring complex on the eastern end of the natural area supply water to the lake and wetlands. Birds present during the breeding season include bald eagle (Haliaeetus leucocephalus), merlin (Falco columbarius), northern harrier (Circus cyaneus), yellow rail (Coturnicops noveboracensis), sandhill crane, Brewer's blackbird, and American bittern (Botaurus lentaginosus). Substantial numbers of migrating shorebirds make use of the property. Bark Bay Slough is owned by the DNR and was designated a State Natural Area in 1977.