The swamp formed in the location of pre-glacial seas and in the bed of a lake that still persisted during the post-glacial period and the beginning of the Holocene. The peat layer is 3–4 meters thick. The central part of the swamp is elevated 60 meters above sea level. There are hummocks (elevated areas) and hollows (depressed areas, with water seeping on their surface); the height difference is 0.3–0.6 meters. The length of the hollows is 2–10 meters, width – 3 meters. Along the edges of the Plynoji, common reed, tussock sedge, rushes, common cotton grass, marsh ragwort, tawny sedge, and among the trees, Scots pine predominates, nearer to the swamp center – common cranberry, Magellan's dwarf rush, tussock sedge, black crowberry, willow, round-leaved and long-leaved sundew, sundew, tussock cottongrass (listed in the Red Book), dwarf pines, curly birches. The swamp is home to black grouse, predatory buzzards, field pipits, cranes. There are deer. The Alanga, Krancia, and Vynija rivers flow out of the swamp.

Installed (2003, updated in 2019) is the Plynoji Educational Trail (length 1.6 kilometers).