a hill or ridge of sand piled up by the wind See also: Dunes in the Great Lakes Region E. coli (Escherichia coli) E. coli is a bacteria naturally found within the intestinal tracts of humans and other animals, and is necessary for proper development and health. Certain strains of E. coli, however, can be extremely harmful, even fatal, if ingested. E. coli is found in human and animal wastes, and can infect drinking water if not properly treated through a wastewater treatment plant.