Ice on pond of Clapham Common

This morning (16th January) the pond in Clapham Common froze and ice covered the whole pond, well... nearly. Some of the birds managed to break through even though when I threw a small stone on the ice it didn't break -  the stone just kept sliding along. If the pond is frozen it means it was 0 degrees or less and when its 0 degrees or less it means that it could snow.