Must have come from the German immigrants that populated the area in a big way in the turn of the century. I lived in Milwaukee for some time and none of that ice cycling survived...... and the Milwaukee River and its banks isn't as "friendly" an environment as it might have been, back in those times...
You do that these days on the Milwaukee River and the boys from the Locust Street police station will most likely be scrambling down the banks and have you on your back in a second for transport to jail. for trespassing.
Maybe one might still search for and find these old ice bikes hidden away in attics and garages in old houses in the area though....