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Natural Creek Conditions

There are times when a creek may look an unusual color and it may not be because of man-made pollution. There are some things that nature produces that temporarily change the look of a creek but do not harm the animals living there.

​Natural Condition ​Description Time of Year​
Pollen in a lake







 ​Pollen from plants, especially trees like pine, can be found in the late spring floating on surface waters. This naturally occurring phenomenon can look like a film on the water or appear as discolored pockets in the water.



 Spring and summer are prime times for pollen deposits.

Tannins in a creek








 This is a natural occurrence caused by the decomposition of organic material such as leaves. Much like steeping a tea bag in a mug, leaves and other organic material release tannins which can cause a stream to turn a dark (sometimes black) color.


 Tannins show up often in autumn especially during the leaf drop.
Tannins also appear in spring when oak trees lose leaves.

Iron Bacteria in a Creek





​Iron Bacteria

​This fuzzy, orange substance is a type of bacteria. It often looks like rust because it oxidizes dissolved iron in groundwater. Oxidation prevents iron from dissolving in the water and produces either an orange colored slime or an oily sheen. One way to tell the difference between a petroleum discharge and iron bacteria is to run a stick through the sheen. If the sheen shatters like glass, it is iron bacteria. If the sheen comes back together, it may be a petroleum spill and should be reported by calling 311.







 A fact sheet with pictures and descriptions of natural creek conditions is available for printing.​​​