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The American Falls shown from Niagara Falls

The U.S. side of the Niagara Falls is pictured in Ontario, January 8, 2014. The frigid air and "polar vortex" that affected about 240 million people in the United States and southern Canada will depart during the second half of this week, and a far-reaching January thaw will begin, according to AccuWeather.com. REUTERS/Aaron Harris (CANADA - Tags: ENVIRONMENT TRAVEL)

Niagara Falls freezes to a stop

The polar vortex bringing chilly temperatures to eastern Canada and the northeastern U.S. was so cold, it caused the world-famous Niagara Falls to stop flowing. Normally, the fast-moving water continues to flow even in sub-zero temperatures, but on January 8, 2014, the top layer of water was frozen solid.