The polar vortex that has gripped the US and Canada this week has led to some spectacular icy images.
The latest come from Niagara Falls, which partially froze when the temperature hit a record low of minus 2 degrees.
Aaron Harris, a photographer for Reuters, took several shots of the 167-foot frozen falls.
The ice formed on the US side of the falls, which straddle the border with Canada.
While unusual, it's not the first time Niagara Falls has frozen.
Photographs from the early- and mid-1900s archived at Niagara Falls Public Library appear to show frozen falls, though some experts have questioned their authenticity.
Of course, the eye-catching freeze did not completely stop water from flowing.
According to EnvironmentalGraffiti.com, only once has freezing weather "caused the thousands of cubic feet of water per second flowing over the Niagara Falls to run dry, an event thought to have been caused by ice jamming and damming upriver," and that was in 1848.
The partial freeze should thaw later this week, according to forecasts, when the temperature at the falls is expected to rise to 46 degrees.
While Harris' photos of the frozen falls are authentic, don't be fooled by some of the old images circulating on Twitter and Facebook.
And this one, posted Tuesday, is actually from 2012.
Several states away, in Michigan, giant ice boulders believed to weigh as much as 75 pounds were found this week floating near the shores of Lake Michigan.
Park Ranger Annie Lipscomb explained how the rounded ice forms when chunks of ice break off the large sheets of ice on the lake. As the waves tumble and pummel the ice, the edges are smoothed and rounded, much the same way stones are shaped.
A blog post from the Atlantic Cities explains that while the snow boulders look strange, they are relatively common around the Great Lakes region.