Lake Michigan has started to freeze. Temperatures were so low that parts of the lake froze over entirely.
Ice quickly formed along the lakeshore.
The cold snap has prompted school and university closures, flight cancellations, and the suspension of mail-delivery services throughout the Midwest.
The lake water has even frozen into odd shapes in some places.
next slide will load in 15 secondsSkip AdSkip AdOver Lake Michigan, a fog has formed. Sometimes called sea smoke or sea fog, this can happen when extremely cold air blows over water that's warmer.
Windchill temperatures in Chicago reached minus 55 degrees Fahrenheit on Wednesday morning, well below the temperature of the water.
Lakeside buoys were encased in ice.
Despite officials' warning of "life-threatening" temperatures, some people have ventured out to take photos.
Ice floes float on the Chicago River, which winds through the city.
next slide will load in 15 secondsSkip AdSkip AdFrostbite can set in within minutes at this extreme cold, according to the National Weather Service. But the cold didn't stop Chicagoans.
More than 1,700 flights were canceled in total between Chicago's two airports, O'Hare and Midway.
Keeping the Metra commuter trains moving was challenging, too.
Workers for Chicago’s commuter rail system went to extreme measures to keep the trains running, lighting fires next to frozen tracks.
The tracks contract in extreme cold, causing breaks in the line — hence the need for extra heat.
next slide will load in 15 secondsSkip AdSkip AdThe weather is Minnesota is perhaps the worst of any US state.
Windchill temperatures hit minus 66 degrees Fahrenheit on Tuesday evening.
The winter weather conditions in Minnesota are causing highway accidents.
The weather in nearby Wisconsin was a little warmer — the overnight low was minus 31 degrees Fahrenheit.
The freezing conditions did not deter some Wisconsin commuters from their daily rides.
next slide will load in 15 secondsSkip AdSkip AdIcicles formed on a railing at the Lake Michigan harbor in Port Washington, Wisconsin this morning. The area experienced minus 50 degree wind chills.
These cold temperatures are a result of the polar vortex — a ring of frigid air that circulates above the Arctic.
Sometimes during the winter, streams of air from that Arctic vortex move south towards the US and Canada.
The National Weather Service expects the polar vortex to continue bringing dangerously low temperatures through at least Friday.