Do the lakes freeze completely during the winter? –LifeSavvy

Have you ever skated on a frozen lake? Or have you even seen a completely frozen lake for the first time? You might be wondering, “Hey, what’s with all the fish?” Well here’s the thing, lakes don’t completely freeze over.

If you’re from a cold climate, this probably doesn’t come as a surprise (or might be if you’ve never thought about it), but that frozen lake isn’t ice all the way to the bottom.

Usually, an upper layer will form in the body of water. It can be weak enough to break at the first sign of weight, or strong enough to host an impromptu ice hockey tournament. This is why you should always check the thickness of the ice and not walk on it unless you are absolutely sure it is safe.

But what determines the thickness of the ice? And why exactly don’t the lakes completely freeze over? Let’s see it.

How does a lake freeze?

A lake is a body of water completely surrounded by land. Most contain fresh water, although saltwater lakes do exist. They come in various sizes and depths and can be found all over the world.

When the outside temperature is consistently above 32 degrees Fahrenheit, most lakes are thermally stratified. This means that warmer water, which has a lower density, settles on the surface, while cooler water, which has a higher density, settles below. As the outside temperature drops, the warm water on the surface begins to cool, and this density difference changes.

Eventually, the exposed water at the lake’s surface cools to 39.2 degrees Fahrenheit, which is the temperature at which the water is most dense. This new density causes the water to sink to the bottom of the lake while the warmer water is pushed to the top. The cycle continues until the outside temperature is cold enough for the top layer of water to drop below 39.2 degrees Fahrenheit and finally freeze below 32 degrees.

Because ice is less dense than water at 39.2 degrees, the ice sheet floats on top of the warmer water below. The colder the outside temperature, the thicker the layer of ice will be. However, ice is a good insulator, and depending on the depth of the lake, it is difficult for the outside temperature to cool enough for the lake to freeze completely. The layer of ice on top protects the liquid below from cold air and keeps it above freezing.

It would take a very shallow lake or an extremely cold winter (think: outer space) for large lakes to completely freeze over.

Why it is important that lakes do not freeze completely

Freshwater habitats, such as lakes, are home to more than 100,000 species of animals and plants. If the lakes were to freeze over completely in the winter, many of those animals and plants would be deprived of oxygen and food and would subsequently die. It would be disastrous if these ecosystems were to start from scratch every year.

The natural process of circulating water during winter also redistributes nutrients and oxygen throughout the lake. Without this fact, the deepest waters would not have enough oxygen to support life.

Fish and other life forms that live in lakes also contain unique adaptive qualities that allow them to survive under the ice. Their metabolisms slow down and they will instinctively reduce their energy expenditure during those months. Some other animals hibernate and some plants survive against all odds. Whether we know why or not, essentially all living creatures are equipped to survive this fascinating phenomenon.

The next time you’re out in the cold and see what appears to be a frozen lake, don’t be too quick to assume it’s safe and approach it with caution.