Those who convert to Catholicism are said to have “swum the Tiber,” referring to the river that runs through Rome. Those who convert to Orthodoxy are said to have “swum the Bosphorus,” the strait in Turkey that separates Europe from Asia. So what is a person swimming who converts to Lutheranism? I have heard “Mississippi” for those who join the Lutheran Church Missouri Synod, based in St. Louis. But Anthony Sacramone gives the definitive solution (whether he came up with it first or someone else did, I don’t know) when he refers to “paddling the Elbe.”
The Elbe river, I learned from Wikipedia, goes through Wittenberg and other important Lutheran sites, such as Torgau and Magdeburg (a Lutheran city whose whole population practically–25,000 men, women, and children–was massacred by the Catholics during the Thirty Year’s War).
I suppose someone who converts to Anglicanism has swum the Thames. A new Calvinist has swum Lake Geneva. (Do people say these already?) Up until recently, when the National Council of Churches lost its Manhattan headquarters, we could say that a theological liberal has swum the Hudson. Is there a Baptist river? A Pentecostal river? A non-denominational river?
For other religions, we could say that a new Hindu has crossed the Ganges. A new Mormon has swum Salt Lake. Can you think of other swimming metaphors like this?