Juvenile, measured at 12 inches long. Note the yellow tail. I overturned some buckets on top of the purple one, which was right next to my patio, to get rid of standing water, and lets just say this lil guy gave me quite a surprise. First three photos are of it alive.
https://herpcenter.ipfw.edu/outreach/Accounts/Viperidae/Agkistrodon/Cottonmouth%20(Agkistrodon%20piscivorus)/CottonmouthFactSheet.pdf