Publishing term--can someone explain it to me?

[Savannah]

I was reading about a poorly edited and published book, described thusly:

When I looked at the text my heart sank. There were lots of very basic errors, things like confusion between its and it’s, confusion between possessives and plurals, “would of” instead of “would have,” lines of text repeated at the bottom of one page and again at the top of the next, outright spelling errors … The typography was so awful that it was difficult to read the text. Lines were frequently dropped, resulting in short pages, and the text had so many rivers it was hard to read an entire page. The publisher made no effort to kern; none at all. There were reversed and unmatched quotation marks, broken ellipses … it was bad.

The text had so many rivers?

Is there anyone with editorial experience who can explain that phrase? Google isn’t helping me here.

[stuyguy]

A river is an old school typography term. It’s when the (white) spaces between words line up line after line after line, so it appears that there is a thin “river” of white space snaking up and down the page. It is considered bad aesthetics to have many or noticable rivers on a page of type.

[Squink]

A river squiggles its.  way about this block of text
A river squiggles its way.   about this block of text
A river squiggles its way in.  this block of text
A river squiggles its way about.   this block.  of text
A river squiggles its way about a.  block of text
A river squiggles its way about.  this block of text
A river squiggles its wayward.  path through this block of text
A river squiggles its way in.   this block of text
A river squiggles its way.   about this block of text
A river squiggles away.  through this block of text

A river is a pattern of blank spaces in successive lines that draws the eye, and distracts a reader from the content of the page.

[Savannah]

Perfect answers, both! Thank you.

Helpful, and damned speedy, too.