Borderline environments may deteriorate to inhospitable conditions. In some places nitrogen levels in the water reach dangerous levels. Still, Park waters remain mostly free of chemical pollutants. However, a disease, giardia, makes the water undrinkable. Dogs, horses, and wild boar help spread this parasite.
All water needs filtration, boiling, or other accepted treatment before drinking.
Pests and disease also threaten the Smokies' ecosystem. Currently the most visible and serious threat is the balsam woolly adelgid. The small wax-covered insect attacks the Park's Fraser fir trees. The fir overreacts to the feeding adelgids, clogging its transport tissues. Trees die within five years of infection.