If you’ve seen a slimy brown residue in your local waterway or drain- it could be iron bacteria, a naturally occurring microorganism.

While it may be unsightly there is no evidence to suggest that it is harmful to our health.

Iron bacteria have been present in natural waterways for over a million years. Iron bacteria feed on iron. When the bacteria are ‘feeding’ they may leave slimy rust-coloured deposits suspended in our creeks, lakes, canals and rivers.

If you live near a waterway you may notice this condition worsens after heavy rainfall. This is a result of iron rich soils leaching into the waterways.

The process

When oxygen, water and iron mix together they can create the right conditions for iron bacteria to bloom. Iron bacteria need to oxidise (change their compound structure) to fulfil their energy requirements. This involves changing ferrous iron (Fe2+) into ferric iron (Fe3+). This process makes the iron insoluble and produces the rust-coloured slimy deposit you may have noticed.

Spotting iron bacteria

Iron bacteria are typically rust coloured, slimy and have an oily appearance on the water’s surface. The bacteria can also break up when disturbed.

Council officers use simple test kits for quick identification or a water sample can be taken for further analysis under the microscope.