Occasionally, by coincidence, the gaps between words on a page of printed text will become aligned, producing “rivers” of white space that descend across multiple lines. These occur most commonly when the font is monospaced and justification is full. Because they’re distracting, these artifacts are generally discouraged; typographers sometimes view a printed page upside down in order to spot them.

In ordinary text long rivers are unlikely, but in 1988 Mark Isaak found the 12-line example above on page 277 of the Harvard Classics edition of Darwin’s The Voyage of the Beagle (squint to see it).

Fritzi Striebel offered a small collection of unusual rivers at the end of this article in the May 1986 issue of Word Ways.