The Susquehanna River, which had been frozen over, is now open, and our lakes and ponds are beginning to thaw. These are all signs that the ice fishing season is coming to an end. The fishermen have had a longer season this year than they usually do.

The winter was cold enough that even Lake Erie was completely frozen over. In years past, the ice had not become thick enough for ice fishing, which prevented most ice fishermen from participating in their sport.

The process is amazing that ponds and lakes go through when freezing and thawing. In the past, I wrote about the process that ponds and lakes go through as they freeze. I wrote that this process is most amazing because water is one of the few liquids that becomes lighter when changing to a solid form.

If this were not so, the world would be locked in an ice age.

The process a pond goes through when thawing in the spring is as amazing as when freezing in the fall. When the sun’s rays become stronger the snow melts; however, the ice remains on the pond. As the temperature becomes warmer, the ice will first melt along the shoreline and next, the shallow parts of the pond.

This is because the Earth collects and holds the heat better than the water, causing this area of the pond to thaw first. Sometimes a pond’s ice will melt quickly, and the pond will open in days. At other times, while the ice is melting, there are days with cold weather and the pond refreezes; however, this new ice is a thin crust and quickly disappears as the temperature rises.

After the ice finally leaves the pond there is a strange occurrence, the water in the pond turns upside down. This is not something that can be seen because it is a very slow process; therefore, the spring “turnover” can only be observed by delicate instruments.

This turnover is the most important event that takes place in ponds or lakes throughout the year. If it were not for this spring turnover, the living animals of the pond might never awaken from their winter’s sleep.

Although water is lighter when it becomes solid, water from melted ice is heavier than the ordinary cold water at the bottom of the pond. As a result, the heavier water from the melted ice settles toward the bottom of the pond.

As this heavier water settles, the cold water from the bottom of the pond is forced to rise towards the surface, which is the cause of the spring turnover.

During the winter, the ice covering the pond stops all oxygen from entering the water, and by the time spring comes, the pond is almost depleted of oxygen. As the ice begins melting it begins to take oxygen from the air, and as the water sinks towards the bottom, oxygen is carried along. If it were not for the new oxygen being carried to the bottom of the pond, the animals, which are hibernating in the mud at the bottom of the pond might not awaken.

The spring winds speed up this turnover by creating currents in the water and rippling and splashing the water in the air, where it can quickly take in oxygen.

One might think that the colder water sinking to the bottom of the pond would keep the animals in hibernation but it is the new supply of oxygen that awakens these animals.

As the cold-water sinks to the bottom, the sun warms the water on top, which in turn makes the water insects active again. The backswimmers, water striders and water beetles are some of the first active insects to appear after the ice melts.

They are in search of food, such as tiny plants, animals and protozoa (single-celled units, which swim in the water).

There are millions of these creatures, which in turn are eaten by water fleas and their relatives. Have you ever looked at a pond where the water appears to be an off-color?

Many times, water fleas are the reason for the water appearing to change to a yellowish or greenish color.

Tiny plants called desmids and diatoms are food for the strange creatures of the pond. The pond’s animal life depends upon these little plants, which are so small they must be seen under a microscope.

Then, one evening as the sun begins to set and the shadows lengthen over the pond, the first calls of the spring peepers can be heard. Their calling is one of the harbingers of spring and a sound that means the countryside will soon be turning green. For the next two months, the calling of the peepers will ring out across the land.

As the pond water is warmed by the sun the frogs and turtles that have been hibernating all winter long awaken. Most fish produce their eggs in the springtime. Now, the pond is full of life. The ducks, geese, herons and others have appeared.

Just as the animals of the fields and forests, the pond dwellers are ready for breeding season, and their cycles of life will begin anew.

Bill Bower is a retired Pennsylvania Game Commission Wildlife Officer. Read his blog and listen to his podcasts on the outdoors at www.onemaningreen.com.