Foam on the water

Published: Oct. 21, 2021 at 9:33 PM CDT
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GREEN BAY, Wis. (WBAY) - If you’ve noticed foam on local waterways, don’t worry. The Wisconsin Department of Natural Resources says it’s harmless.

Just as the leaves change color every year, waterways mix things up -- literally.

Madeline Magee, the beach program manager for the DNR, described, “Wind can physically take water that at the top of the lake and push it to the bottom of the lake, and then we have water from the bottom of the lake move on up to the top of the lake.”

Usually, surface water is too warm to mix with what’s below.

“The reason it has this upper layer and this lower layer is that warm water is less dense than cold water,” Magee explained. “When that water is stratified during the summer, not only does it prevent mixing but anything that sinks down to the bottom stays there because it doesn’t have a way to move back up.”

But as the temperature drops -- “The air is colder. There is less light. The water is probably colder, too” -- so does its density. “As the water gets closer together in density, it becomes easier for the wind to mix the water.”

And that causes the water to mix up easier, creating a little foam.

“That foam is all of the organic material -- dead plants, dead fish, all that kind of stuff -- that sinks to the bottom.”

The DNR says that foam is harmless to all and nothing to be scared of.

Magee said, “99% of the time it is totally natural and it won’t hurt you. There are other things that could cause foam and be problematic, but most of the time that is not the case.”

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