The Bog Turtle is considered to be the smallest turtle native to the United States. It averages in size from 3 inches to a record length of 4.5 inches. Many populations of Bog Turtles now have less than 20 individuals, and some have fewer than 10. Although habitat destruction is the major threat to the Bog Turtle populations, pesticides, fertilizer run-off, water pollution and species collection also have significant impact. Invasion of exotic plants into Bog Turtle habitats in some areas has impacted the turtles by the non-native plants forming dense patches of vegetation, which impede movement and produce shade.