A search at CDNOW finds these songs:
"Flood Blues" performed by Sippie Wallace and Louis Armstrong.
"Flood Water Blues" performed by Lonnie Johnson.
"Flood Water Blues" performed by Casey Bill Weldon.
"Florida Flood Blues" performed by Ruby Gowdy.
"High Water Flood Blues" performed by Carl Martin and Willie Blackwell.
"Mississippi Flood Blues" performed by Joe Pullum.
"Southern Flood Blues" performed by Big Bill Broonzy.
"Terrible Flood Blues" performed by Big Bill Broonzy.

I played the sound sample for the Sippie Wallace song, and I could transcribe only the single repeated line:
"The water is rising, people fleeing for the hills"
--but it certainly sounds like the one GUEST,Karen was looking for (17 months ago).