How to identify it
Slender garter snake 46-102 cm long whose colour varies: pale gray with alternating rows of darker side blotches, dark brown with less distinct borders, or nearly all black. [1][2][3]
Yellow dorsal stripe may be present, confined to the neck, very indistinct or absent; throat and belly whitish to yellow. [1][2][3]
One morph is blue-gray with a faint olive dorsal stripe and white dots along the sides; another has a yellow stripe and black side spots. [1][2][3]
Closely tied to streams: basks on streamside rocks and banks and retreats into the water. [1][2][3]
Compared with the sierra gartersnake (thamnophis couchii): Distinguished mainly by range: Sierra gartersnake is the Sierra Nevada species, aquatic gartersnake the Coast Ranges species; both were once lumped as T. couchii. [1][2][3]
Compared with the terrestrial gartersnake (thamnophis elegans): Formally distinct species (Rossman and Stewart 1987); aquatic gartersnake forages almost entirely in and along streams, terrestrial also occurs in deserts, meadows and forests. [1][2][3]
Species it is confused with
Check these before deciding what you are looking at. If you are not certain what it is, do not shoot.
- Sierra gartersnake · Thamnophis couchii
- Terrestrial gartersnake · Thamnophis elegans
Field notes
Where it lives
Rocky fast-flowing streams, sluggish soft-bottomed streams, ponds, small lakes and adjacent riparian zone, within woodlands, woodland-grass edges or chaparral; usually tied closely to water but sometimes travels on land. [1][2][3]
How it behaves
Active diurnal snake that basks on streamside rocks or vegetation and flees rapidly into the water when disturbed. [1][2][3]
Forages in and along streams for fish (especially trout and sculpins), tadpoles, frogs, salamanders and their larvae; also leeches and earthworms. [1][2][3]
May be active in any month but is most often found April-July; mates in spring and gives birth to live young, August-October, in secluded sites such as under bark. [1][2][3]
Seeks cover under water beneath rocks or among exposed tree roots. [1][2][3]
Limited legal take
Legal take of this species exists only under narrow conditions — a quota, a draw, a permit, a small area, or animals released or held on private land — set by the authorities below. Nowhere else is a legal opportunity implied, and Hunt shows one only where a certified rule establishes it.
Where legal take is listed
- California — reptile take · 2026 California Freshwater Sport Fishing Regulations (updated July 10, 2026), 14 CCR 5.05/5.60
Being listed is not an open season. Seasons, zones, licences, methods and limits decide whether this animal may be taken on a given day and place — check Hunt or the authority before you go. Listings read 2026-09-30.
Where it is found
Southwestern Oregon and western California north of Point Conception (Coast Ranges from the Oregon border to central Santa Barbara County), from sea level to about 1,920 m; absent from the Salinas Valley. Not in Canada.
Sources
Every claim above is attributed to one of these published sources.
NatureServe · reviewed 2026-09-30
NatureServe
California Department of Fish and Wildlife · reviewed 2026-09-30
California Department of Fish and Wildlife
Wikipedia · reviewed 2026-09-30
Wikipedia