Iron bacteria are long thread-like bacteria that secrete slime, occur naturally, and "feed" on iron in water and soil. Unlike most bacteria that get their energy from decomposing organic matter, iron bacteria get their energy from oxidizing ferrous iron.
What causes it?
Iron bacteria are caused by a combination of minerals, chemistry, and biology. Iron is a common element in Pacific Northwest soils, and when it combines with oxygen and water, there is the potential for iron bacteria to form. When the dissolved iron reacts with oxygen in the air, it forms rust-colored iron oxides. These deposits often occur on hot, dry days when the water is sluggish. You may also notice a foul, swampy odor, similar to the smell of rotten vegetables.
What does it look like?
Iron bacteria form rust-colored slimy or stringy deposits in or on the surface of puddles or slow-moving water. They can also leave rust-colored stains on concrete, patios, sidewalks, and other hard surfaces.
You may also see an oily sheen on the water's surface. The oily sheens created by the decomposing bacteria cells are often mistake for petroleum sheens, but they are quite different. Iron bacteria sheens break apart and don't come back together when disturbed. Poke the surface of a sheen with a stick or throw a pebble at it. If it breaks apart and doesn't come back together, it's likely iron bacteria.
Is iron bacteria harmful?
Although water with iron bacteria usually looks strange and alarming, these bacteria are a natural occurrence and are not dangerous to people or our waterways. Iron bacteria are not raw sewage or hazardous material.
How do I get rid of it?
Sometimes you can replace iron-rich soils with fill that has lower iron content, but this may be costly and have other environmental impacts. Because iron bacteria are not harmful, the best thing to do is wait for the water to clear. After a rainstorm, dissipation often occurs.
What if it doesn't look like iron bacteria? What if I think it's pollution?
If you disturb a sheen and it comes back together, or if you think what you're seeing is something other than iron bacteria, please call our Spill Hotline at 425-806-6750 so we can investigate. You can also check this list of pollution examples to know if it's something you should report.