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What is the foam like stuff that washes up on our beach on the Saginaw Bay?
from Shannon of Faith Lutheran School in Bay City, Michigan, Age 9

While the foam that washes up on shore may look like the foam in your kitchen sink, lake foam is usually a naturally occurring phenomenon and not caused by pollution. Foam is created when the surface tension of water (the attraction of water molecules for each other, which gives a drop of water its round shape) is broken down and air is mixed in, causing bubbles. Surface tension can be reduced by natural organic compounds as well as pollutants, such as soaps and detergents.

Natural organic compounds are released into the water by decomposing algae and fish. As wind stirs the water, air is mixed in with the water because of its reduced surface tension, and foam is produced. Foam will often collect in large quantities on windward shores, and that's why you may see foam on the beach. Natural foam may have a dirty brown color, and will smell earthy or fishy.

Foam from detergents and soaps is now uncommon, although this was not always the case. In the 1950's and 60's, most detergent was non-biodegradable (not able to be broken down by bacteria). This type of detergent made great suds, but caused a lot of water pollution. Fortunately, most detergents made today are biodegradable, so they are unable to produce the long-lasting foam found on shorelines. Foam from detergents will have a perfumey smell.

We used the following references, so read on if you want to learn more:
Foam - A Cause for Concern?
Lake Foam - Environmental Fact Sheet
Foaming of Surface Waters - A Natural Phenomenon on Ontario Lakes

Thank you for your question!

Answered on July 17, 2000

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