Have you ever wondered about the white foam that forms on the beach where heavy waves break in response to the first storms of fall? Or have you ever wondered about foam on river banks or lakes?

Healthy Alaska rivers have foam

Standing at Grael’s landing, I overheard many tourists over the years being upset about the “pollution” on the river. They were referring to small spots of foam on the water. Sometimes even 5 cent size dots of foam float downstream in summer.

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When you kayak or canoe or travel on Alaska rivers or go fishing at Alaska rivers or lakes, you often see foam on river banks, or collected at fallen trees in the water. The foam is part of the river’s ecosystem, and no reason at all to be upset about. However, I have to admit, it is icky, but for another reason than being pollution.

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Foam is made up from lipid molecules of decay

Don’t freak out about foam on the river, lake or at the beach. It is nature made, and a sign of healthy waters. The foam builds during decomposition of dead animals like dead fishes, water insects, amphibian, larvae, feathers from water birds, etc. and plant material including leaves that fell into the water.

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Foam consists of fat oil molecules so-called lipid molecules. They once were the waterproof walls of plant cells or skins of creatures. As you know, oils and fats do not mix with water. They are also lighter than water. Therefore, the lipid molecules float as a thin film on the water.

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Two Alaska rivers, the Chena River (foreground) and Tanana River (background) with wind driven waves in the rain

Wind produces waves when it attacks the water surface. The waves stir the water and with it the thin oily film. Consequently, air mixes with the oily, fatty film on the water. Bubbles form starting the foam development.

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In areas, where the flow is slow or (temporarily) absent like on beaches, river banks, at trees fallen into the water, or at beaver constructions, foam can accumulate. There, the water can look like someone had dumped their dish water. The foam is an unexpected view and experience for Alaska visitors.


Finally, bacteria feed on the foam and, so to speak, clean up. The life cycle of eating and being eaten closes again providing new material for new foam on the water.

Color varies depending on uptake of material

While natural foam from decay is white, uptake of debris, pollen, spores, algae, silt and dirt can change its color. Yellow foam, for instance, most likely contains pollen.

Natural foam differs from pollution caused foam

If the foam where from detergents or soaps, the foam would have some scent. Natural foam smells rotten, if at all.

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When you found this post interesting you may also like to read about funnel clouds in Alaska or faults in Denali Park. You can find the full collection of Focus Alaska posts in the Archive.
Photos: G. Kramm

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