Rust in the Water

The sight of furry orange growth or rust-colored slime in a stream can be alarming, and might naturally lead you to suspect a contaminant or pollutant in the water. In fact, such sightings are usually iron oxide deposits (sometimes called “iron ochre”) that have formed as a byproduct of iron bacteria metabolism. This fuzzy coating of iron oxide is produced when iron in the water is metabolized by specific iron bacteria species. Iron bacteria can be found in lakes, ponds, and streams throughout Georgia. The presence of iron oxide deposits is indicative of iron-rich groundwater and/or acidic soil. Iron bacteria can also cause an oily film or rainbow sheen on the surface of the water, another byproduct of the bacteria’s metabolic process. Unless there is a sudden, unusual appearance of this film, it does not indicate a contamination event. If you’re concerned about a petroleum spill, poke the sheen with a stick. If the sheen swirls back together immediately, it’s petroleum. If the sheen breaks apart and does not flow back together, it’s from bacteria or other natural sources. Iron oxide deposits in wells can cause unpleasant odor and taste and impair well equipment function, but in natural water bodies there is no need to treat or remove the deposits. While they are unattractive, iron oxide deposits pose no known health or environmental risk.