What's that Floating Lake Foam ?
By Jan Quaine

Have you ever been leisurely boating or walking along the lakeshore enjoying the day only to be greeted by a white soap like floating foam? What in the world is it and where did it come from?

You might be interested to know that there are two types of foam: natural foam and foam from some type of pollution.

Natural foam is created when the surface tension (attraction of water molecules or strong bonding) is reduced. Decomposing water plants release a variety of organic compounds in the water. These organic compounds are surfactants, which reduce the surface tension of the water. This allows the wind and wave action to mix air with the water creating foam, which frequently collects on the downwind shore. It is not very pleasing to look at but if it is natural foam it is harmless. Foam is often seen in the morning and may disappear in the afternoon. In the fall when there is a general dying and decomposing of aquatic plants and algae the increased decomposition increases foam. Since zebra muscles came into our lake, you may see an increase of foam. This invasive species seems to be excreting large amounts of surfactants, which reduce surface tension into the water or their feces fertilize the growth of algae and other aquatic plants which eventually dieback. Both of these may be the reason that with the introduction of the zebra muscles in our water also came an increase of lake foam.

Foam caused by pollutants comes from detergents that leech or are discharged into the lake. The law now prescribes phosphorus free washing machine soaps but that isn’t the case with dishwasher detergent. Many of these contain high levels of phosphorus. If you have difficulty purchasing phosphate free detergents you may follow this recipe for dishwasher soap: 1 cup Borax Plus mixed with ½ cup baking soda.

How can you tell the difference between the naturally occurring foam and the detergent caused type? Put some foamy water in a jar with a tight fitting lid. Shake vigorously. If the foam subsides, it is most likely naturally occurring. If the foam does not dissipate, it is probably from some type of pollutant. Natural foam will also smell “fishy” while pollutant foam may smell like scented soap. While it is comforting to know that most of the foam is natural, we all need to be aware that it could be a sign of water pollution.

Source of information: Michigan Department of Natural Resources, Tip of the Mitt Watershed Council