If you have seen a reddish-brown sediment, stain or substance in your local waterway or stormwater drains, don’t be alarmed. The chances are that this is being caused by iron bacteria, which is a naturally occurring micro-organism.
The bacteria oxidises the iron (or manganese) in the presence of dissolved oxygen which forms a-rust, hence the colour.
When flows are low it accumulates, but it clears up when sufficient flows can flush it away. During the initial phases of iron bacteria activity, there may be a decaying swamp smell and an oily appearance on the surface of the water. There should not be a smell of petrol, oil, sewerage or chemicals.
The oily appearance is merely attributed to the harmless chemical reaction taking place in the water and “fractures” when it is broken with a stick which distinguished it from other forms of oily substances.
If you are concerned, call the EPA Pollution Line on 13 15 55 or Council on 02 4868 0888.
Iron Bacteria Fact Sheet(PDF, 329KB)