A little story to add to Mark’s Harvard story. I used to drive along the Charles River to work everyday. It's does freeze in the winter. One morning I noticed three flat bottom powerboats breaking up the ice with poles. My first thought was that someone fell threw ice and it was a search and rescue. On my way home I found out what was going on. They were the Harvard sailing team breaking the ice so they could sail. They cleared about a football size area with a small path to the dock. I think there were about ten boats sailing.