image of icon bacteria

Iron bacteria blooms in Blue Mountains given wet period

11 Apr 2022

The sustained and excessive wet period has resulted in Iron bacteria blooms appearing in several areas across the Blue Mountains. This harmless bacterium visually resembles an oil slick.

Iron bacteria (also known as Iron-oxidizing bacteria) are bacteria that live underground, feed on iron-rich water and create an orange or rust coloured slime. Ground water is low in oxygen, and this limits the growth of bacteria, however when groundwater rises to the surface via creeks, cracks and pipes, the oxygen in the air acts like a fertiliser for the bacteria and it can grow quickly leaving a rust coloured and slippery slime in the water.

"The sustained and excessive wet period has resulted in the presence of iron bacteria flocculates appearing as orange blooms,” Mayor Mark Greenhill said. “Iron bacteria is not dangerous and poses no health risk to the community.

“It is, however, very slippery, so care should be taken when walking in and around bodies of water that contain iron bacteria.”

Iron bacteria looks unappealing and is often mistaken for an oil spill, but poses no environmental risk as it is naturally occurring. However, in extreme and rare cases, it has been known to overgrow and block water infrastructure.

“Iron bacteria is often mistaken for an oil spill. It stains the ground with an orange-brown colour that looks like rust and has slimly pieces of fluff,” Mayor Greenhill said. “In still or stagnant water, the bacteria can create a film on the surface of the water that has a rainbow sheen, that is almost identical to oil.”

The easiest way to tell the difference is by using a stick to break the surface sheen. Iron bacteria will crack and separate, whereas oil will clump and stick.

Common areas for iron bacteria blooms to occur include creeks that are fed by groundwater, steep slopes where water seeps out from the ground and water infrastructure (such as piping/guttering) that have groundwater sources.

Download the fact sheet on Iron bacteria

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