|Foam on Bull Creek|
|Foam on the shoreline of a lake, created by wave action - Photo from The Waterline|
"On lakes, in bathtubs and in mugs of beer, the cause for foam is the same. Agitation at the surface causes air to get under the surface film of the water. Weakened surface tension is unable to force the air out, but rather keeps water wrapped around a volume of air, creating a bubble. If this happens for long enough, foam is created. On lakes, the agitation is usually due to wind, and the resulting foam will collect on the downwind side of the lake. In streams you will see the foam in eddies or floating downstream, and it is created by the flow of the water disturbing the surface film."The quote above is from the Waterline which goes on to describe in detail how foam is formed. It describes the relationship of surface tension, aeration, and particles in the water to foam formation. Not all foam is benign as organic compounds from decomposing plant or animal matter and other pollutants can make foam appear more commonly. Rather than attempt an explanation, go to the Waterline story for details.
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