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Jeffrey C. Davis, Aquatic Ecologist
The Aquatic Restoration and Research Institute
Alaska Clean Water Action Grant No. 05-02

Foam often is seen accumulating against logs or on the banks of streams, or along the shores of lakes on windy days. When it first appears, foam can be white, but generally turns brown over time. The development of foam occurs due to changes in the water surface tension and the physical introduction of air. There is a slight tension on the surface of water caused by the chemical attraction among water molecules. This tension is what allows some insects to move along the water surface and what causes water to “bead up” on your car during a rain storm. Certain molecules interact with the water reducing the surface tension. These molecules are called surface active agents or surfactants. Foam is produced as air, introduced in the turbulence of stream riffles, below waterfalls, or as waves break upon the shore, bubbles to the water surface.

Human Sources
There are many natural and synthetic (human produced) surfactant molecules. Synthetically produced surfactants are an ingredient of most household cleaning products such as detergents, shampoos, toothpaste, and cosmetics. Early detergents, developed after the Second World War, were non-biodegradable, that is they could not be broken down by bacteria. This resulted in large accumulations of persistent foam particularly below sewage treatment plants and other points where these surfactants were released into waterways. These early detergents also contained phosphorus which softened the water by binding with calcium and magnesium. However, this phosphorus also contributed to blooms or prolific growths of algae and other aquatic plants. Due to these problems, the chemical structure of synthetic surfactants was modified to a biodegradable form that contains sulfates instead of phosphates. The most widely used synthetic surfactants today are linear alkylbenzenesulfonates (LAS) listed on most products as sodium or ammonium laureth or lauryl sulfate.

Natural Sources
Naturally produced organic surfactants are released from algae and plants when they die and begin to decompose but also in lesser amount when living. These organic surfactants are part of a large variety of plant material that when dissolved in water is referred to as dissolved organic carbon (DOC). The breakdown of large algal blooms in ocean waters can lead to the accumulation of foam on beaches up to 3 feet deep. The primary source of DOC in lakes and streams is from the surrounding watershed soils. Bogs and wetlands deliver large amounts of DOC to streams and lakes because they are very productive and the breakdown of plant material within wetlands is slow. The presence of DOC in lakes and streams is why they are dark in color and often referred to as “brown-water streams.” Foam often is seen in our brown-water streams in the spring as snowmelt carries DOC to adjacent streams and lakes or during fall rain storms after the leaves have fallen and begun to decompose. In addition to causing foam, DOC provides energy and performs many additional functions important to aquatic ecosystems. Although natural, human activities that cause an increase in algae or aquatic plant growth like the introduction of nitrogen or phosphorus fertilizers can cause plant and algae blooms and an increase in foam production along with the removal of oxygen as these plants decompose. The foam is not toxic; however, removal of oxygen can cause fish kills.

Determining Causes
Foam from plant produced surfactants will occur at many locations along a stream accumulating on against the bank, or on logs or other material in the stream. It may be white at first, but will turn brown over time as sediment particles build up in the foam. The foam will persist for some time gradually diminishing in size. Increases in foam abundance will often follow rainstorms that transport the surfactants to the stream or along lake shores on windy days.

Foam from detergents and other synthetic surfactants generally will accumulate near the source and should not occur over large distances. The foam will be white and sweet smelling or scented. The foam will not persist, and will dissipate quickly once the source is removed. Foam accumulations from synthetic surfactants will generally not be related to rain storms or windy conditions on lakes.


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Fact Sheet: Foam. 2004. Indiana Department of Environmental Management, Office of Water Quality Assessment Branch.

Fendinger, J.J., D.J. Versteeg, E Weeg, S. Dyer, and R.A. Rapaport. 1994. Environmental behavior and fate of anionic surfactants. In, Environmental Chemistry of Lakes and Reservoirs, L.A. Baker (ed.). American Chemical Society, Washington D.C.

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Maryland Department of Natural Resources. 2004. Harmful Algae Blooms in Maryland.

Wegner, C., and M. Haburger. 2002. Occurrence of stable foam in the Upper Rhine River caused by plant-derived surfactants. Environmental Science and Technology 36:3250-3256.

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Talkeetna, AlaskaRestoration, Research, Conservation

ARRI - Aquatic Restoration & Research Institute, Talkeetna, Alaska


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