Iron bacteria - Shoalhaven City Council

Iron bacteria

What is it?

There are several forms of natural bacteria that grow and multiply in water and use dissolved iron as part of their metabolism.

They oxidise iron into its insoluble ferric state (RUST) and deposit it in the slimy gelatinous material that surrounds their cells.

By-products form this process form an oil-like sheen on top of the water.

Have you ever been down to your local creek and seen a reddish-brown or even orange coloured material on the rocks and reeds in the bottom of the creek?

You may also nave noticed something that looks like oil on top of the water in the same location.

Sometimes you may see the same things where water is seeping out of the ground.

Chances are, what you are seeing is NATURAL.

Places where you are most likely to see iron bacteria
  • On rocks near waterfalls
  • Where sandstone has been crushed and used as fill for roads etc.
  • On steep slopes where water seeps out of the ground
  • Creeks that are fed by groundwater (water flowing under the surface) 

  • Why is it happening?

    Surface water and groundwater in the Shoalhaven is naturally high in dissolved iron because of the types of rocks found in some areas in which we live.

    (i.e. Ironstone) Our waters are also generally high in dissolved oxygen - perfect conditions for the iron bacteria to thrive in!

    Checking that it is Iron Bacteria

    There are a couple of things that you can check whether the stuff you are looking at is iron bacteria.

    1. It should not SMELL TOXIC
    It is possible that you might smell something that you might associate with decaying matter in a swamp.  This is OK, as it is likely that the bacteria are dying (especially if they are being dried out in the sun).  You should not be smelling things like petrol, oil, chemicals or sewerage.

    2. The STICK TEST
    Poke a stick into the material that looks like an oily film on top of the water.  If it fractures like ice on a pond and doesn't join back together then it is probably associated with the iron bacteria.  IF IT CLINGS TO YOUR STICK AND JOINS BACK TOGETHER THEN IT COULD BE OIL. (If the situation warrants it, call the EPA Pollution Line 13 15 55 or Council's Environmental Health Section 4429 3453)

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