2026-Feb-20
The Myth of Ice Thickness: Staying Safe During the Thaw
As the sun gets stronger and the days get longer, the ice on Georgian Bay undergoes a dangerous transformation. What was a solid, predictable surface becomes “rotten ice”—a state where thickness is no longer a reliable measure of safety.
The Science of the Soften: What is “Rotten Ice”?
When air temperatures fluctuate to near or above freezing, the crystal structure of the ice begins to break down. This process, called honeycombing, occurs when water and air pockets infiltrate the vertical grain of the ice. Even if the ice measures 10 inches thick, if it is honeycombed, it has reduced lateral strength and can collapse under your weight like a house of cards.
While mid-winter ice is typically clear and “blue,” late winter ice can take on a dull grey or black appearance. This indicates that the ice is saturated with water and has lost its structural integrity. Even if it measures 10 inches thick, grey ice may not support the weight of a single person.
Watch the video below to find out more about how ice conditions change:
Hidden Hazards: The “Bottom-Up” Melt
Ice doesn’t just melt from the sun hitting the surface; it also softens from the bottom. Moving currents underneath the surface constantly erode the ice from below, which can make it much thinner than it appears. Additionally, dark objects such as rocks, logs, and dock pilings absorb solar energy and radiating it back into the surrounding ice, causing it to thin significantly faster than the open lake. This process is often hidden by late-season snowfalls, which act as a thermal blanket; this insulation traps ground heat and prevents the ice from refreezing, even when overnight air temperatures drop well below freezing.
Three Major Indicators of Danger
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Grey/Dark Colour: Dull grey or black ice is a sure sign that water is present. This ice is “rotten” and will not support significant weight.
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The “Shoreline Gap”: Shorelines melt first. Rocks, logs, and docks absorb solar heat and radiate it into the ice. If the edge is mushy, the rest of the bay is likely unstable.
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Hollow Sounds: If your footsteps or “thumps” with a spud bar sound hollow or crunchy rather than a solid “thud,” the ice is structurally failing.
If you’ve assessed the ice and are venturing out, you should always:
- Check with local authorities for warnings about unsafe conditions
- Watch the weather, as temperature fluctuations and precipitation may soften the ice
- Never travel on ice alone and always ensure you have told someone where you are planning to go and your return time
- Keep away from unfamiliar paths or unknown ice and avoid traveling on ice at night
- Wear appropriate clothing (watertight drysuit and PFD) and proper equipment (ice picks)
- Tip: wear your PFD and keep ice picks around your neck rather than in a bag. If you fall in, your fingers will go numb within minutes; you need these tools within reach to pull yourself out!
- Avoid slushy ice, untracked ice or ice near moving waters or dock bubblers