Photographers and gawkers are gathering around the Straits of Mackinac right now. The narrow waterways between Michigan's upper and lower peninsula are currently home to a rare blue ice formation, tailor-made for Instagram addicts. (Or, you know, people who just enjoy nature with their eyes. They exist.)
The straits flow under the Mackinac Bridge, along the Mackinaw City shore. There, blue-hued ice is piling up in an otherworldly fashion. This ice forms when lake water freezes without bubbles trapped in the ice. When there are bubbles present, light is scattered as it passes through. In the absence of bubbles, light can shine straight through the ice.
George Leshkevich of NOAA's Great Lakes Environmental Research Laboratory told Michigan's WFMY that the lack of bubbles allows "short wavelength light to penetrate and scatter in the water below and reflect back through the ice."