The New York Times is baffled by the existence of a nude beach on a riverbank in rural Wisconsin:
MAZOMANIE, Wis. — America’s Dairyland seems an odd setting for a nude beach. Its short summers and swarms of mosquitoes are hardly in keeping with the palm-tree paradise that “free” bathing brings to mind. ...
And yet for decades, nudists have basked on Mazo Beach, a secluded sandbank on the lower Wisconsin River about 30 miles northwest of Madison. With estimates as high as 70,000 visitors a year, the spot, which is owned by the state, has become one of the largest nude beaches in the country that is not on a coastline, weathering angry protesters, conservative politicians and wary neighbors along the way.
It shouldn't be surprising. Wisconsin is the most German state in America, and nudism was one of many Life Reform movements that popped up in Germany in the late 19th Century.
Sci-fi writer Robert A. Heinlein, for example, was a classic German-American dualist: an engineer and military officer who was also into nudism and a lot of other such stuff that briefly made him a hippie icon in the late 1960s. His 1951 novel The Puppet Masters can be read both as a classic alien invasion thriller and as a huge plot contrivance to force the U.S. Government order all the women in America to walk around without any clothes on (Operation Sun Tan).