Why does St Lawrence Seaway in North America freeze?
When the temperature falls well below freezing moving water can often avoid freezing. However, at the edges of the flow (walls of channel, etc.) motion is almost stagnant and freezing can commence and grow out toward the middle of the channel where velocity is greatest eventually covering the channel. Ice is a relatively good insulator and it is unlikely that the entire channel will freeze solid. It is dangerous to walk on ice with water flowing under it. Someone told me that they say a person fall through thin ice on Boston’s Charles River. He was swept away from the hole and people watched helplessly as the victim moved along clawing at the ice from below.
