The verse of a version of Shenandoah mentioned by blamith is from Joanna C. Colcord, "Songs of American Ssilormen."

Missouri she's a mighty river;
When she rolls down her topsails shiver.

She says: "This is a late corrupted form, and was the one used on American ships after the Civil War. The words, as will be seen, are simply nonsense, but it was one of the best known and most frequently used of the capstan shanties. The tune is very free in its rhythms, and cannot be written in one tempo.
Whall gives the earlier version, which was the story of how a white trader courted the daughter of the famous Indian chieftain Shenandoah, and bore her away in his canoe 'cross the wide Missouri.'

"He says: "The seaman of to-day knows nothing of this old song except the tune and one line, "Oh, Shenandore, I love your daughter."...
Originally it was a song, not a shanty, and had nothing to do with salt water... It probably came from the American or Canadian voyageurs, who were great singers....""

To simplify, trying to make sense of nonsense simply adds more nonsense.