In February, cold winds brought very low temperatures to North America. The Niagara Falls, which are one of the best tourist attractions in the US, froze.
The falls did not freeze completely, but they looked so. Thick ice made a crust on the falls, but the water was still flowing under the ice. The falls cannot freeze because there is too much water in them, and the water is very strong. It can never stop flowing.
The water stopped flowing only once in history. It happened when ice from Lake Eerie blocked the flow, so only little water was flowing in the falls. It cannot happen again because there is a special construction on the river which stops the ice.
You can watch the original video in the Level 3 section.