Cracks on the ice

You better mind those cracks while skating. If you don't pay attention to what's below your feet you might hit one of them and lose your balance. The ice is still strong though. Even today they maintained the ice with a tractor. I don't know why they were doing it though. Looked like they were clearing snow (or actually small ice particles which the skaters release from the ice surface constantly). But today it was a very windy day and wind had already cleared all snow from the skating track.