The ice's natural crystalline structure is changed by constant freezing and thawing. Ice does not freeze at a uniform rate. It may be a foot thick in one spot, and just an inch thick only ten feet away. A layer of snow can insulate the ice underneath, slowing down the ice-forming process, making a stroll across the lake potentially dangerous. Ice near the shore is weaker.
Ice forming over flowing water is most dangerous, especially rivers, streams, or spring-fed lakes.
Use common sense. Take a few minutes to observe the ice. Safe . . .