Some communities on the east side of Houston have red worms in their water and I read about something really bad that would infect you if it went up your nose. Don’t remember any details.
http://www.cbsnews.com/news/killer-amoeba-found-in-louisiana-water-system/
Inadequate disinfection of the municipal water supply is the problem there.
Also a problem if you swim in rivers, ponds and other surface water in warm winter areas.