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Why Don’t Fish Freeze in the Winter?

Stepping out into the deep freeze that is Iowa in the winter, it can be hard to believe that much can make it in the often below-zero temperatures. And with ice so thick that heavy-duty trucks can drive out on a lake, how can a fish possibly survive below?

First, ice forms at the surface first, not from the bottom up. While some small creeks can freeze all the way through, that’s not the case for most lakes and rivers. Once the water is at about 39 degrees Fahrenheit throughout the lake, it’s ready to start freezing. As air temperatures drop, the water on top of the lake begins to freeze once it hits 32 degrees. Since ice is less dense than the warmer water below, the ice stays on top of the lake instead of sinking.

Still, that’s really cold water below, right? It’s not a problem for fish because they’re cold-blooded. Their body temperature is the same temperature as the water.  

The colder water does slow fish down, so they don’t need to eat as much or swim a lot. Just as we’re more likely to curl up on the couch on a cold winter night, fish spend most of the winter just hanging out.

Since fish don’t freeze, ice fishing is a great outdoor activity in the winter. If you’re a bit more warm-blooded, mark your calendars for Free Fishing Weekend, the first full weekend in June. On these days, Iowa residents don’t need a fishing license. All other fishing laws remain in effect.

Learn how fish survive the cold temperatures of winter | Iowa DNR

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