Thamnophis atratus

The aquatic garter snake (Thamnophis atratus) is a species of colubrid snake. Three subspecies are currently recognized. It is found exclusively along the coast of Oregon and California. Thamnophis atratus grows up to 18-40 inches (46–102 cm) long. Its dorsal coloration varies greatly. The different coloration patterns are: pale gray with alternating rows of darker blotches on the sides, dark brown with borders that are less distinct, or nearly all black. A long yellow stripe running down the back may be present or absent, only confined to the neck, or just very indistinct. The throat and underside of the snake are whitish to yellow. One variety of this snake has a blue-gray background color with a faint olive-colored dorsal stripe and white dots along its sides. Another morph has a yellow dorsal stripe with black spots along its sides. The second variation has the more classic garter snake look; however, due to its behavior and scalation, it is grouped in this species.