I remember the winter of 1962-3.
Mother had always warned us of the 'bottomless' spring which fed the millpond at Leatherhead. Even in the hardest winters the centre of the pond would remain a stretch of unfrozen moving water where the ducks crowded together but that winter, for the only time I can remember, the millpond froze over completely. Cautiously we advanced onto the ice and eventually stood looking down through the crystal clear ice directly into the wide opening of the spring below where the weeds were still moving in a flow of water!