Take care with this one. For a long time I was under the impression that the Big Muddy was the Mississippi. I don't know where I got this idea from, but it appears that it's at best only partly right. Wikipedia says that the Missouri is the Big Muddy; other sources say that the Mississippi is also known by this nickname. There's also a river that's actually called the Big Muddy River, which is 156 miles long and joins the Mississippi in southern Illinois.
There's a famous song by Pete Seeger, entitled Waist Deep in the Big Muddy. It's an anti–war song, written at the time of the Vietnam War, and doesn't specify which river it's referring to, although it does mention Louisiana. (The Missouri doesn't flow through Louisiana, but the Mississippi does.) Seeger's song was censored when he sang it on a recording for an American television comedy and variety programme in 1967. Bruce Springsteen used the line "Waist deep in the Big Muddy" as the chorus for his song, The Big Muddy (on the 1992 album Lucky Town).
© Haydn Thompson 2017