Shortly after Delia Owens’s “Where the Crawdads Sing” was published last Aug. 14, Reese Witherspoon picked it as a selection for her Hello Sunshine book club, telling The Times she “loved every page of it.” It was a lucky break. The debut novel — which had a solid first printing of 27,500 — landed at No. 9 on the paper’s best-seller list on Sept. 16.

Then the book, about a young girl surviving alone in a coastal North Carolina marsh, did something unusual. Instead of lingering at the bottom of the list for a few weeks before slipping off altogether, as a small novel might be expected to do, “Where the Crawdads Sing” started to climb — and climb, and climb — finally reaching No. 1 on Jan. 20, which is where you can still find it today. It has now been on the list for 29 weeks.

So what happened? How has a small literary novel flourished while hyped books by big-name authors have flashed on and off the list? “Reese’s pick skyrocketed awareness,” says Alexis Welby, the publicity director of Putnam, “and the word-of-mouth just continued to grow from there.” Readers, she says, “just have to push the book into the hands of others so they can talk about it.” It’s now been rated over 125,000 times on Goodreads and has a 5-star rating on Amazon, where it’s been reviewed more than 7,400 times.