“Usually lake or river ice is not that transparent, as numerous small air bubbles are formed inside the ice upon freezing,” Dr. Kuhs said. But occasionally, he added, “larger portions of the ice can grow bubble-free with the air accumulated in separated portions; in fact, some larger bubbles are seen in some of the enlarged ‘jewel’ crystals.”

This may be the only spot to find this kind of river ice, but you can probably spot glacier ice that looks similar in southern Chilean fjords or Alaskan panhandle inlets, Dr. Wadhams said.

The best time to see jewelry ice is in January or February. And the optimal time of day depends on what colors you want to see. As the sun rises and sets, the ice appears orange. During the day, it’s blue. Jewel ice can also appear sapphire, topaz or opal, depending on the sky. In Toyokoro, the town where the ice shows up, locals go to the beach and post frequent updates about the state of the ice on Toyokoro’s website. The last update, posted on Jan. 25, revealed that the temperature was minus 11 degrees Fahrenheit and the ice was covered in snow.