Foam in the Creeks

I have so often wondered what causes foam in the creeks, but I always forget to look it up.  Today, I was going through some old photos and found this one, which I took specifically to remind me to look it up:

Foam in Creek

Here’s what I found out:

The surface tension of the water is reduced by a surface active agent, also known as a surfactant.  This reduced surface tension causes air to be trapped into tiny bubbles at the surface in areas where there is turbulence in the water thus creating foam.  The foam starts out white, but will turn brown as particles of sediment get caught in there, too.

The surfactants can be either man-made or natural.  Man-made surfactants include chemicals present in many household cleaning products.  According to Jeffrey Davis, an aquatic ecologist:

The most widely used synthetic surfactants today are linear alkylbenzenesulfonates (LAS) listed on most products as sodium or ammonium laureth or lauryl sulfate.

If the foam you find in your creek is localized and sweet-smelling, perhaps someone washed their hair or dishes!  If the foam has a fishy or more earthy smell, then suspect a natural cause.

The natural surfactant is called DOC (dissolved organic carbon).  DOC comes from the decomposition of a wide variety of plant material including algae and aquatic plants, but also the leaves from trees that line the creek.  Foam caused by DOC is often widespread, occuring in more than one spot along the creek.  You may see more foam after a wind or rain storm as more organic material is washed into the creek and the water is running faster causing more turbulence.

Foam in the Creek Foam in the Creek

So there you have it!  Now you know.  You can be such a smarty pants next time you are hiking with friends and they ask about the foam!


13 thoughts on “Foam in the Creeks

  1. I got scared by the word “benzene” which I saw neatly tucked into the middle of the word “alkylbenzenesulfonates” and even more frightened when I realized what it is called on most product labels because it’s in many of the products I use to cleanse my body.

  2. Very cool and interesting – thanks for taking the time to look it up and share it with us. I have seen creek foam, and I also observed a similar phenomenon along the shore of a lake up in Michigan once, caused by the same thing, I’m sure.

  3. I frequently walk across the Rainbow Bridge connecting Niagara Falls New York and Niagara Falls Ontario and have seen foam in the lower Niagara River. I wonder if it is caused the same way?

  4. @Jim – Probably. One of the articles I listed above described foam along the seashore that can be 3 feet deep… all caused “naturally”. Of course, some unnatural things – like too much fertilizer that runs off into the water – can cause (unnaturally large?) algal blooms… which decompose and cause foam… so… hmm….

  5. Pingback: Black Knot « A Passion for Nature

  6. Oh – Jennifer – the more I investigate your website, the more I like your observations and ways of describing them. When I was a kid and camped with my family in the Allegheny National Forest near Marienville, PA, we used to tell my little sister the foam in the eddys of Salmon Creek was created from fishermen upstream spitting in the water. After that she would no longer wade in any watershed that showed signs of foam on it’s surface. Thanks for conjuring up that long lost memory. – Dave

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