They came down from the clear blue sky

A chilly night had frozen the wet snow and that, combined with the nice weather, meant it was a good day to ski on the lake.
Towards the end of the trip I came across these strange tracks, leading across about 100 meters of snow-covered lake and ending at the edge of the icewhere a narrow strip of open water started.
What beast left such a strange track?
Yesterday's blip (from a different lake) gives the game away. A small group of swans had waddled across the wet snow and dropped into the open water.  Swans have big feet! 
Three long toes, each ending in a claw, and webbing between.