Thamnophis couchii
Silhouette: Alex Slavenko · PhyloPic
In 3 days ~40% in a week ~70%
Thamnophis couchii, commonly known as Couch's garter snake, the Sierra garter snake, or the western aquatic garter snake, is a highly aquatic species of snake in the family Colubridae. The species is endemic to the western United States, specifically the Sierra Nevada mountain range.
The specific name couchii is in honor of Darius Nash Couch, a U.S. Army officer and naturalist who collected specimens during the Mexican-American War and subsequent expeditions. The Sierra garter snake is a medium-sized, slender snake adapted for an aquatic lifestyle. They possess a somewhat pointed head, which aids in underwater foraging in fast-flowing currents. Like many garter snakes, they have a mild venom produced in the Duvernoy's gland that is harmless to humans but effective at subduing small, cold-blooded prey. Furthermore, because their diet frequently includes highly toxic newts, the snakes can sequester the tetrodotoxin in their own tissues, making them poisonous to potential predators like birds and mammals.
T. couchii is native to California with a small population in west-central Nevada and the Owens Valley. It is predominantly... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Sequoia and Kings Canyon National Parks | 🇺🇸 United States | |
| 2 | Yosemite National Park | 🇺🇸 United States |
Possible
About 20% of wildlife watchers report a Western Aquatic Garter Snake sighting in Yosemite National Park on a given day, based on 59 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 8th most-seen of the 17 reptiles we can rate there. Over three days the chance rises to about 40%, and over a week to about 70%, if each day is a fresh chance.
March to July
In those months about 20% of wildlife watchers report a Western Aquatic Garter Snake in Yosemite National Park on a given day, against under 5% in November to February, the lowest months.
Between 1 and 4 pm
Across all the parks we cover, that three-hour window holds the most Western Aquatic Garter Snake sightings with a recorded time, and about 9 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
2nd of 2
Of the 2 parks where we can rate Western Aquatic Garter Snake sightings, Yosemite National Park ranks 2nd at about 20%. The best odds are in Sequoia and Kings Canyon National Parks (United States, about 30%).
GBIF citizen-science records
It is estimated from how often the Western Aquatic Garter Snake is recorded against all the reptiles logged in Yosemite National Park (59 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
