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Probably the worst sign of organic pollution in a stream is when normal green or brown streambed algae become replaced by colourless slimes formed by Sphaerotilus bacteria, commonly known as “sewage fungus”. This bacterium requires organic waste to feed on and it has been found below leakages/discharges of raw sewage, silage pit leachates, and wastes from dairy factories, meat processing plants, chicken farms and pulp mills. Sewage fungus is generally considered to be unacceptable in any stream or river, so such growths should be reported to your council pollution hotline. Examples of “sewage fungus” growths are shown below: