A warning has been issued after an enormous lake and big tourist attraction froze over for the first time in decades.
The park rangers of Emerald Bay in California have said that the startling blue-green lake is now completely covered in ice.
While the frozen body of water may be beautiful, they are fearful that visitors to the park may be tempted to step onto the frosty sheet.
To protect people from inadvertently falling into the frigid waters, the park has been closed to visitors until the ice melts.
"Mother Nature can be destructive and beautiful," the park said in a statement. "For the 1st time in decades, Emerald Bay has frozen over, as seen in photos captured by our staff. Enjoy these breath-taking photos until it’s safe to visit -- the park is closed & road closures are in place."
It may be the first time in three decades that the bay has frozen to this extent, according to California State Parks.
The last time is thought to have been in the early 1990s.
This year an exceptionally cold winter has led roads in the area to be closed down due to too much snow, while the ski resorts have also been shut due to safety concerns.
The depth of the water and the usual temperatures in the area mean that it Emerald Bay only freezes over completely very rarely.
The ice on its is only a few inches thick and certainly not sturdy enough to walk on without any fear of falling in.
The bay was created sometime in the Pleistocene Epoch, which lasted from 1.8 million to 11,500 years ago, by glaciers pulverising rock and forming a depression.
It is a National Natural Landmark, part of a program which recognizes and encourages the conservation of outstanding examples of the natural history of the United States.
In Sweden, where the country's many lakes regularly freeze over completely, many school children are given an unusual education in cold water safety.
Each year secondary school children (armed with permission slips from parents) troop down to the local lake when it's sufficiently frozen over and take turns throwing themselves into a hole chain-sawed into the ice.
"We lived right out by the coast, and my parents (as well as many others) thought it was important that we knew how to handle not just falling into the water and getting out, but also have experience with the cold," Alexandra Högborg, who grew up in Malmo, explained.
"A part of the training was also how to survive after getting up from the water. Like heating yourself up, because the air is almost always colder than the water it self.
"It was a real risk, like every year some kid did fall through the ice. So it was definitely important."
Ice safety is taken very serious in Sweden, particularly in the north, where the country's great lakes form migratory routes for reindeer herds and moose, and hockey rinks for the people.
Unlike in the UK - where incidents such as the Solihull lake tragedy are mercifully rare - tales of people getting in trouble on the ice or falling through are much more common.
