Australian Weather Calendar: May 2017
Mario Mirabile was holidaying at Bogong Village in Victoria's high country, in August 2015, when he spotted sheets of ice around nearby Lake Guy.
Ice can form on a lake when the surface becomes cool enough. Ice crystals are most often hexagonal in shape, and they grow much faster out of the corners of the hexagon than out of its flat sides. Long needles grow outwards from the centre of a crystal, then ice fills in the area between the needles. This results in the feather-like shapes seen in Mario's photo.