This is a watersnake on the Harpeth river outside Nashville, Tennessee. Potentially a cottonmouth (Agkistrodon piscivorus)
Date May 2006
Author Chinmay7
Source: https://commons.wikimedia.org/wiki/File:Watersnake_cottonmouth_tennessee.png

The cottonmouth (Agkistrodon piscivorus), also known as water moccasin, swamp moccasin, black moccasin, cottonmouth, gapper, or simply viper, is a venomous snake, a species of pit viper, found in the southeastern United States. Adults are large and capable of delivering a painful and potentially fatal bite. The generic name is derived from the Greek words ancistro (hooked) and odon (tooth), and the specific name comes from the Latin piscis (fish) and voro (to eat); thus, the scientific name translates into “hooked-tooth fish-eater”.
Order: Squamata
Suborder: Serpentes
Family: Viperidae
Genus: Agkistrodon
Species: Agkistrodon piscivorus (Lacépède, 1789)
Synonyms:
Vipera aquatica (not a binomial) Catesby, 1743
Crotalus Piscivorus Lacépède, 1789
Crotalus Aquaticus Bonnaterre, 1790
Scytale piscivora — Sonnini & Latreille, 1801
Coluber Aquaticus — Shaw, 1802
Ancistrodon piscivorus — Cope, 1860
Ancistrodon pugnax Cope, 1860
Trigonocephalus piscivorus var. pugnax — Jan, 1863
Vipera Cenchris Piscivorus — Higgins, 1873
Ancistrodon piscivorus Lacépède, ssp. piscivorus — Cope, 1875
Ancistrodon piscivorus Lacépède, ssp. pugnax — Cope, 1875
Ancistrodon piscivorus piscivorus — Yarrow, 1882
Ancistrodon piscivorus pugnax — Yarrow, 1882
Ancistrodon piscivorus Var. pugnax — Garman, 1884
Agkistrodon piscivorus — Garman, 1890
Ancistrodon piscivorus — Boulenger, 1896
Agkistrodon piscivorus piscivorus — Gloyd & Conant, 1943
Ancistrodon piscivorus piscivorus — Schmidt, 1953
Agkistrodon piscivorus laurae Stewart, 1974
Agkistrodon piscivorus — Gloyd & Conant, 1990