If you’ve seen a slimy brown material in your local waterway or drain- it could be iron bacteria, a naturally occurring microorganism. While it may be unsightly it is not harmful to health. Iron bacteria have lived in our waterways for over a million years. Iron bacteria feed on iron. When the bacteria are ‘feeding’ they may leave a slimy rust-coloured or a rainbow sheen on the surface of creeks, rivers or stormwater systems fed by ground water.

If you live near a waterway, you may notice its worse after heavy rainfall. This is because iron rich soils are entering the waterways. It's important to remember that iron bacteria are not harmful to our health, and they do not adversely affect our waterways.

The Process

When oxygen, water and iron mix together they can create the right conditions for iron bacteria to grow. Iron bacteria ‘feed’ on iron within the water. The iron bacteria ‘feeding’ makes the rust-coloured slimy deposit or rainbow sheen you may have seen.

Spotting Iron Bacteria

Iron bacteria are normally rust coloured and slimy, with a rainbow sheen on the water’s surface, which looks a lot like oil or petrol. The bacteria will normally break up when disturbed. Council officers use a simple test to see if the sheen is oil or iron bacteria. A stick is run through the rainbow sheen and if it breaks apart it is iron bacteria, if it quickly reforms and clings to the stick, it is likely to be oil.