On a recent salmon spawner survey, I stopped to watch a big mound of foam spinning in circles in a stream eddy. Why was I seeing foam in a stream reach that I thought was healthy; a reach surrounded by a diverse, older forest? After that, I started noticing numerous patches of foam every time I monitored my assigned section of stream.

It turns out lots of people ask that same question. Fortunately, the accumulations of foam I saw in the back eddies of the stream, usually associated with a protruding log or pile of woody debris, are a sign of healthy, natural processes at work.

When autumn leaves and woody debris decompose, they release organic compounds that include lipids (natural oils) and fatty acids. These compounds, similar in chemical composition to soap, break the surface tension of water, allowing air bubbles created by turbulent water to accumulate on the surface. Fall rains may also transport organic compounds from surrounding forest soils into the water.

Curiosity led me to dig a little deeper into surface tension and why the bubbles linger.

Water molecules are strongly attracted to each other, creating surface tension. Surface tension is what prevents a slightly overfull cup of water from overflowing, why water “beads up” on your car during a rain storm and allows insects to skate across the surface of a pond. Compounds that reduce surface tension are called surfactants. They lower surface tension by increasing the distance between water molecules, reducing the strength of the molecular attraction of water molecules toward each other.

Bubbles are formed when a thin layer of water molecules surrounds some air, creating a sphere. Both the inside and outside of the “bubble skin” water layer is coated with a layer of surfactant molecules; those molecules have one end attracted to the water layer and the other end of the surfactant molecule pointed away from it. Bubbles burst when the layer of water between the surfactant layers evaporates. Some compounds (think glycerin added to detergent) or colder temperatures slow down the evaporation process, so the bubbles last longer.

Sometimes stream foam IS caused by contaminants. How can you tell the difference?

Consider its color, smell and location. Natural foam is usually persistent, off-white or tan in color and might have an “earthy” odor (although the foam I smelled had no fragrance at all.) You’ll find natural foam in water bodies with high levels of organic debris. Human-made foam, on the other hand, tends to be white in color, with a perfumy (from detergent discharge) or unpleasant (septic field failure) odor. Sometimes it is also sticky to the touch, and its presence is not associated with recent rainfall events.

I hope this increases your appreciation for the presence of foam in streams or along a beach. Maybe you’ll even join me in taking an extra moment to play with the quivering foamy bubbles, knowing they are all part of nature’s process.

Brandywine Conservancy

Bubble Science for Kids

Geophysical Institute at University of Alaska Fairbanks

(Learning about stream life by studying what’s in foam)

The Redoubt Reporter

Join us January 28-29 and February 18-19 to plant native trees and shrubs at the Jamestown S'Klallam Tribe's Caldero side channel site on the Dungeness River!

It will be a festive occasion with hot cocoa, coffee and treats. NOSC sweatshirts, beanies and other merchandise will be available for sale, by cash or check only.

Please RSVP below for all dates you plan to attend! You can check our website and follow us on social media for further information and opportunities.

Join us Wednesday evening at the Hilltop Tavern (2510 W Sims Way, Port Townsend) from 7 to 9 pm for the final NOSC Bingo of the year. Play, laugh, and have a grand ol’ time while supporting NOSC. We can’t wait to see you there!