Water reaches its maximum density at 39.2 degrees Fahrenheit. Then it sinks, displacing less dense water that then moves to the surface. Out in the middle, Dickey Lake is about 70 feet deep (74′ at the deepest point). My shallow pond quickly cools to 39.2 degrees F throughout, then further cooling at the surface makes the water less dense, so the surface water stays in place and ice forms quickly across the pond.
The same process exists in Dickey Lake – but the greater depth and volume of water challenges a warm winter to chill the entire lake to 39.2F. The water escalator continues to move the dense water toward the bottom, releasing warmer water for the surface – while ground temperature doesn’t warm the water significantly in the summer, it does provide a small amount of warming in the winter, but not important.
The ice across Dickey Lake, and which day the lake freezes is basically controlled by the simple fact that water reaches its maximum density at 39.2 degrees Fahrenheit. As the ice melts in the spring, that heavier, warmer water sinks away from it.
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