Science in Everyday Life #1 – How Do Fish Survive Under a Frozen Lake?

 Everyday Science, Everyday Wonder

Simple questions, smart explanations.

A Winter Mystery Explained by Science

Have you ever seen a frozen lake in winter and wondered,
“What’s happening under the ice?”
It may seem quiet and lifeless, but the truth is surprising. Beneath the frozen surface, fish are alive and well — and science helps explain how.

In this first post of our “Science in Everyday Life” series, let’s explore the cold world under a frozen lake.

A Frozen Lake Is Not Really Frozen Inside

When the temperature drops in winter, the surface of a lake begins to freeze. But the ice doesn’t freeze all the way down.
Why?

Because water behaves in a special way: it is heaviest at 4°C. That means the water at this temperature sinks to the bottom. Ice, which is lighter, floats on top and forms a layer. This ice layer acts like a blanket and keeps the water underneath from getting colder.

So, even in the middle of winter, the bottom of the lake stays around 4°C — just warm enough for fish to survive.

Fish Go Into Energy-Saving Mode

To survive the winter, fish don’t need heaters or shelter. They simply slow everything down.

• They stop swimming and stay still near the lake bottom.

• Their heart rate and breathing slow down.

• They need less food and less oxygen.

This is called a state of dormancy — similar to a light sleep. The cold water helps their body save energy, just like a phone switching to battery-saving mode.

Even though the lake looks silent, fish are resting quietly below.

Some Fish Have Special Winter Protection

In places like the Arctic and Antarctic, some fish go one step further.
They produce special proteins in their blood that act like antifreeze. These proteins stop ice crystals from forming inside their bodies, so their blood stays liquid even in freezing water.

In most Korean lakes, fish don’t need these special proteins. The ice layer and the 4°C water below are enough for them to survive the season.

Nature's Smart Survival Plan

What seems frozen and lifeless is actually full of quiet life.
Thanks to the science of water and the amazing abilities of fish, life goes on under the ice.

Next time you see a frozen lake, take a moment to imagine the calm world beneath it — where fish wait for spring in peaceful stillness.

This is just the beginning of our journey into everyday science.
In the next post, we’ll explore another question from daily life:
Why does your breath look like smoke on a cold day?

Stay curious — science is all around you.