Lakes freeze from the top down. Ice is less dense than water, which is why ice floats. The density of liquid water is determined by its temperature, and water is most dense at about 40 F.

Why is that important? As winter sets in, lakes lose energy to the atmosphere, and water near the surface cools, becomes more dense, and sinks. Warmer, less dense water under the surface will rise to replace this surface water. When the entire lake reaches 40 F, the surface water cools further, dropping below 40 F. Because this water is now less dense than the surrounding water, it will stay on the top and continue to cool.

Once the surface water falls to 32 F, it freezes. The freezing then spreads downward into the lake and the ice thickens. Unless the lake is very shallow, you will find liquid water below the ice. This deeper water is about 40 F; fortunately fish can live in this cold temperature.

Freezing first occurs along the shoreline, where the water is shallow. Before ice can form on the surface, the entire water column must first reach 40 F, which is likely to first occur along the shoreline.

Some lake-dwellers use the Coors lite two-stage Cold Activation Method to determine ice thickness by placing a bottle in the lake and letting the ice form around it. They believe that when the 'super cold' on the bottle turns blue, the ice is safe. This is not recommended due to it's not being true, it just means your beer is cold - super cold.

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Less than three inches of clear blue ice

This ice is unsafe! Ice under three inches can break any time under the weight of an average person. Some people may tell you that on cross country skis or snowshoes as little as two inches of ice can hold you up because your weight is distributed better, we think that is pretty bad advice.

Three to five inches of clear blue ice

This ice is capable of holding up a human safely. If you are traveling in a group be sure to spread out as several people standing together will put stress
on the ice.

Six to eight inches of clear blue ice

This ice is capable of holding a group of people or equipment like an ice fishing shack or skimobile. This is the minimum thickness needed if your plans including playing a hockey game or other group activity.

Eight to twelve inches of clear blue ice

This ice is capable of holding up the weight of a car. But ask yourself, "do I really want to drive my car onto the ice," and if it did a submarine imitation how would you explain it to your insurance agent. A car creates a pressure wave as it moves across the surface of the ice. If the water is four feet deep driving any faster than nine miles an hour can shatter the ice around you. The pressure wave advancing under the ice becomes so strong it strikes the lake bottom and returns to the surface, cracking the ice. The deeper the water, the faster you can go. Also be sure that you don't park in the same place for long and keep cars spaced out at least two hundred feet apart, especially when parking. As the car sits in a parked location the ice will start to sag.

Ice thickness isn't a constant on a body of water. Snow cover actually acts like a blanket insulating the water below. Springs and currents can create areas of extreme thickness and patches that are just wafer thin. Snow cover also hides the surface and can mask rotten ice and thin spots. You should always be cautious as you move across snow-covered ice.

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What should you do? First, try not to panic. This may be easier said than done, unless you have worked out a survival plan in advance. Read through these steps so that you can be prepared.

Don't remove your winter clothing. Heavy clothes won't drag you down, but instead can trap air to provide warmth and flotation. This is especially true with a snowmobile suit.

1. Turn toward the direction you came. That’s probably the strongest ice.


2. Place your hands and arms on the unbroken surface. This is where a pair of nails, sharpened screwdrivers or ice picks come in handy in providing the extra traction you need to pull yourself up onto the ice.


3. Kick your feet and dig in your ice picks to work your way back onto the solid ice. If your clothes have trapped a lot of water, you may have to lift yourself partially out of the water on your elbows to let the water drain before starting forward.


4. Lie flat on the ice once you are out and roll away from the hole to keep your weight spread out. This may help prevent you from breaking through again.


5. Get to a warm, dry, sheltered area and re-warm yourself immediately. In moderate to severe cases of cold water hypothermia, you must seek medical attention. Cold blood trapped in your extremities can come rushing back to your heart after you begin to re-warm. The shock of the chilled blood may cause ventricular fibrillation leading to a heart attack and death! 

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