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On days like today, we will sometimes receive calls about pollution in the Occoquan River after individuals observe something like what you see in the photo below, which I took earlier today. Although not generally considered attractive, the off-white, brownish suds in the river are not man-made pollution, but reflect what is most often a harmless, natural occurrence, the accumulation of dissolved organic carbon (DOC). Caused by the breakdown of organic debris from plants and animals in the river, DOC reduces the surface tension of the water making it easier for the associated foam to form. Particularly noticeable after storms when there is a greater flow of water and wind, the foam tends to be more prevalent in the fall when the leaves are falling and in the spring with pollen and the loss of plant buds.
Another natural chemical process also sometimes generates calls to us about orange slime in streams or along the banks of the Occoquan. Again, however, this orange slime is not typically from man-made pollution, but reflects the natural action of bacteria that takes iron from the ground and oxidizes it, essentially preventing the iron from dissolving in the water.
Off course, human activities like nutrient runoff can create algae blooms that might ultimately increase the amount of DOC in waterways, but what you see in the Occoquan River today is simply a regular natural process that you will be able to observe multiple times throughout the year.
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