Iron bacteria

Iron bacteria shows up as a rusty colored gunk in this spring.  This spring is just a few steps from Wildcat Creek in Tippecanoe County.  Probably what is happening is that sewage from houses on higher ground nearby is leaking into the groundwater.  As bacteria feed on the organic matter from the sewage they deplete the oxygen available in the ground.  As there is organic material still available, anaerobic bacteria start feeding, but instead of using a respiration process requiring oxygen, they convert ferric ion (+3) to ferrous ion (+2):

        H2O + Fe2O3 → 2Fe(OH)2 + O2
        (water) + (Iron[III] oxide) → (Iron[II] hydroxide) + (oxygen)

http://en.wikipedia.org/wiki/Microbial_metabolism#Other_inorganic_electron_acceptors

Then when the deoxygenated ground water emerges to the surface at the spring, the high concentration of ferrous ion in solution provides food for iron bacteria.  Iron bacteria do use oxygen as an electron acceptor in their respiration process (as we humans do in ours) but they use the energy difference in the two states of iron for power, rather than most other life forms that use the energy in carbon bonds.

        2Fe(OH)2 + O2 → H2O + Fe2O3
        (Iron[II] hydroxide) + (oxygen) → (water) + (Iron[III] oxide)

http://en.wikipedia.org/wiki/Iron_bacteria

The iron bacteria themselves have no color, the reddish stuff is the bacteria's waste product, an insoluble precipitate of ferric oxide.

Photo taken Feb. 13, 2015.