Aquatic garter snake (Thamnophis atratus)

Mildly venomous but not dangerous: the aquatic garter snake has enlarged rear teeth and a mild venom for its prey, and a bite causes at most local swelling, which is why many sources simply call it harmless. It is not a pit viper or coral snake, the only U.S. land snakes with medically dangerous venom. Clean any bite like a small wound.

The aquatic garter snake's U.S. record is concentrated: California alone holds 93% of licensed records. It is listed in 2 states in all; the next are Oregon (268).

Across the U.S., observation records of the aquatic garter snake run mostly March through October, peaking in May with 21% of them. Winter (December to February) holds 5% of them.

California holds 3,727 licensed records, the 5th most recorded of 46 snakes listed there. Its observation records in California run mostly March through October, peaking in May; most licensed records come from Santa Cruz County, Mendocino County and Marin County. Next come Humboldt County (305) and San Mateo County (265).

Oregon holds 268 licensed records, the 6th most recorded of 16 snakes listed there. Most of its licensed records in Oregon come from Jackson County, Josephine County and Curry County. Next come Douglas County (25) and Coos County (11).

The aquatic garter snake record leans on older material: only 9% of dated U.S. records come from 2017–2026, and the median record is from 1980. The oldest dated record is from 1860; the busiest year was 2001, with 248 records.

Of the 20 counties where the aquatic garter snake is most recorded, 15 are also top counties for each of the first three snakes in the table below; no other snake shares more. Venomous species among its neighbors: the western rattlesnake.

Other species of the genus Thamnophis with profiles here: Western terrestrial garter snake, Common garter snake, Western ribbon snake, Northwestern garter snake, Western aquatic garter snake, Plains garter snake, Checkered garter snake and Eastern ribbonsnake.