Lake Akan may be known for its hot spring, but something cooler is bubbling under the surface.

Ice bubbles were seen beneath the frozen surface of the lake, located in Kushiro, Japan, on Sunday. These are formed when gas rising from the bottom of the lake is trapped by the ice, according to the Akankohan Eco Museum Centre. A worker at the centre said the ice on some parts of the lake is thin, and urged visitors to take extra care, according to The Japan News.

Lake Akan is a tourist attraction in the eastern Hokkaido area and is well known for its natural monument "marimo", a type of floating green algae ball, and sockeye salmon that inhabit the lake.

Surrounded by mountains and volcanoes, the lake has an amazing natural scenic landscape that changes with each of the four seasons - Japanese skunk cabbages in spring, vast forests in summer, red leaves in autumn and the silver snowy landscape in winter.