a mix between mud butt and swamp ass. often happens during strenuous activity where the anal cavity sweats and a small shart slips out, and the sweat makes the small shart turd turn into a marshland of sweat and shit.
"man, i was lifting weights the other day and i was straining, and when i got home, i had marsh ass!"
by Doo Doo Crew January 25, 2009