Listed as Least Concern in view of its wide distribution, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a threatened category.

This species occurs in southwestern United States and northern Mexico. Its range in the United States includes central and eastern Arizona and west-central New Mexico in the Mogollon Rim area. The Mexican range is larger and is disjunct from that in the United States. In Mexico it ranges from northern Sonora and Chihuahua and southward in the Sierra Madre Occidental to central Durango, with an apparently disjunct population in southwestern Durango. It occurs at elevations of 700 to 2,430 m asl (Rosen and Schwalbe 1988, Tanner 1990, Rossman et al. 1996, Arizona Game and Fish Department 1997, Stebbins 2003).

The New Mexican distribution includes the Gila and San Francisco river drainages in Catron, Grant, and Hidalgo counties, at elevations of 1,125 to 2,100 m asl (Degenhardt et al. 1996, New Mexico Department of Game and Fish 1997).

In Arizona, this species occurs in upland drainages in central and eastern Arizona from the White Mountains and along the Mogollon Rim to Oak Creek Canyon, in Apache, Coconino, Gila, Graham, Greenlee, Navajo, and Yavapai counties; good populations found at Oak Creek Canyon and along the East Verde River (New Mexico Department of Game and Fish 1997; Arizona Game and Fish Department, 2002, unpublished abstract compiled and edited by the Heritage Data Management System ). A previously eliminated population from Fort Valley Creek at the Museum of Northern Arizona, Flagstaff, may have been reintroduced (Rosen and Schwalbe 1988).

The population status and trend in Mexico, which includes the bulk of the range, is unknown. However, The Nature Conservancy's Heritage Program in Sonora estimated over 100 occurrences with possibly 80% of occurrences in good condition (A. Villareal Lazarraga pers. comm. 1998).

In the United States, the number of distinct occurrences or subpopulations has not been determined using consistent criteria but probably there are at least several dozen. The Arizona Natural Heritage Program has recorded at least 51 occurrences, a few of which are believed to be not extant (Sabra Schwartz pers. comm. 1998). Degenhardt et al. (1996) mapped 27 collection sites in New Mexico. Its conservation status in Mexico is poorly known (Rossman et al. 1996). Tanner (1990) mapped six collection sites in New Mexico and 23 collection sites in Mexico.

The total adult population size is unknown but is probably at least several thousand. A 1985-1986 survey of 79 locations in Arizona yielded 157 individuals from 10 localities; a crude statewide abundance estimate indicated a population size of possibly fewer than 3,500 non-neonates (Rosen and Schwalbe 1988). According to the authors, this preliminary estimate indicated surprisingly low abundance in Arizona. Additionally, there have been few recent observations during statewide and national forest surveys for sensitive herps in Arizona (Kulby 1995).

In Arizona, some populations appear stable, while others have declined. A 1985-1986 survey conducted by Rosen and Schwalbe (1988) in selected regions of Arizona indicated that the species is nowhere abundant and has been nearly eliminated from some areas where formerly it was abundant. The species is believed to be extirpated from Flagstaff [see range comment] and Wall Lake, Arizona, and from adjacent parts of the East Fork of the Gila River in New Mexico (Rosen and Schwalbe 1988). It has declined along the lower portions of Oak Creek, Arizona, where it is now scarce below Oak Creek Canyon, and apparently has declined in lower Oak Creek Canyon (Rosen and Schwalbe 1988, Kulby 1995, Nowak and Santana-Bendix 2002, Nowak 2005). Additionally, there have been few observations during recent statewide and national forest surveys for sensitive riparian herps in Arizona.

This species is regarded as one of the most aquatic of all garter snakes (Conant 1963). It often occurs along well-lit sections of rocky streams with abundant riparian vegetation, in areas of pinyon-juniper, oak-pine, or ponderosa pine; it basks on rocks, shrubs, or snags, and it often seeks cover under rocks in or adjacent to water (Fleharty 1967, Stebbins 1985, 2003; Rosen and Schwalbe 1988; Rossman et al. 1996). This snake may be numerous among rocks in areas with riffles, deep pools, and abundant large boulders, whereas areas with broad expanses of small rock and sand, and streams that traverse meadows, do not appear to be suitable habitat (Fitzgerald 1986, Degenhardt et al. 1996). Along Oak Creek, Arizona, hibernation occurs from November to April in rocky areas well above the floodplain (Nowak and Santana-Bendix 2002, Nowak 2005).

The greatest threats are introduced predators (bullfrogs, fishes, crayfish), loss of habitat (urbanization, overgrazing, and the destruction of rivers and wetlands), habitat fragmentation, and, in some areas (e.g., Oak Creek, Arizona), habitat degradation caused by heavy recreational use (Rosen and Schwalbe 1988, Nowak and Santana-Bendix 2002, Nowak 2005).

There is indirect evidence that the introduction of bullfrogs (Lithobates catesbeianus) has eliminated populations in some areas (see New Mexico Department of Game and Fish 1997). Additionally, low densities and historical declines in the White Mountains correlate closely with the history of fish introductions (Rosen and Schwalbe 1988). Populations may also be negatively affected by predation by introduced crayfish, which also may negatively affect the snake's prey base (Rosen and Fernandez 1996, Nowak and Sanatana-Bendix 2002, Nowak 2005).

Habitat alteration can negatively affect high-elevation populations. The greater need to thermoregulate at higher elevations makes optimal basking sites such as shrubs and snags essential. Under such circumstances, channelization or other activities that remove or disrupt bank vegetation may lead to extirpation (Rosen and Schwalbe 1988).

A notable concern is the isolation of the central Arizona populations in Oak Creek Canyon and East Verde River. The absence of a mainstream population makes repopulation of these streams during local extinction events highly unlikely. This also implies that the East Verde and Oak Creek populations are irreplaceable and that further degradation of the main streams of the Salt, Black, and Gila rivers may eventually eliminate most, if not all populations in these drainages (Rosen and Schwalbe 1988).

Needless killing and excessive collecting may be having a negative impact (New Mexico Department of Game and Fish 1997). There are indications of regular killing and removal along Oak Creek Canyon, Arizona. An estimated 44% of annual mortality of non-neonates is attributed to human mortality (Rosen and Schwalbe 1988).

This species is regarded as not very threatened by the Sonora, Mexico, Heritage Program (A. Villareal Lazarraga pers. comm. 1998). However, this does not cover all of the Mexican range, and the United States populations appear to be moderately threatened. The degree of threat warrants further investigation.

Apparently there are few if any adequately protected occurrences of this species. The degree of threat (e.g, interactions with non-native fish species) is in need of further study. Better information on abundance, number of occurrences, and population trend is needed, especially in Mexico. If the species is declining in Mexico in the same way as has been recorded on the United States, it might qualify for listing as Near Threatened, or even Vulnerable, under criterion A2.