Scientists aren't really sure, said MSU-Bozeman microbiologist Gordon McFeters.
Some scientists think water is involved.
McFeters did a study of algae that grow in the summer months and form a biofilm, or slime, on rocks of a pristine alpine stream. As the algae mature and die off, organisms like E. coli can grow in the nutrient bed, he said. I'm not surprised by anything anymore. Many kinds of E. coli exist in nature and in our bodies, and without them we wouldn't be healthy. It's a complicated process and a learned one.