Native gartersnakes are the most common aquatic snakes in California. They are often observed
swimming in creeks, ponds, and lakes, from the coast to high in the mountains.
Many but not all native gartersnakes
have a prominant, light-colored stripe that runs down their back. Most are dark colored; a few have rows of
dark spots. Gartersnakes tend to be slender and light in weight.
In the mountainous areas of California, such as the Sierra Nevada range, gartersnakes are the only aquatic species. While all snakes can swim, and will enter water to cool off or to escape people or predators, only gartersnakes will spend many hours in the water. If you observed a swimming snake in a mountainous area, nine times out of ten it will have been a native gartersnake. Probably the most common gartersnake observed in the mountains of Northern California, such as in the Yuba River area, is the Sierra gartersnake (Thamnophis couchii). The Sierra gartersnake (left photo below) is typically dark brown, and often does not have a clearly visible stripe down its back. The Western terrestrial gartersnake (right photo below) also lacks a stripe
You can see other photos of Sierra gartersnakes at the California Herps website. |
In California, Non-Native Watersnakes have never been observed outside of lowland areas.
There are no verified sightings of watersnakes in any natural mountain waters. Some believe that non-native watersnakes can only survive in altered, disturbed, or unnatural habitats, such as agricultural areas, reservoirs, and urban landscapes.
All verified sightings of non-native watersnakes in California have been from man-made or disturbed habitats. The freshwater creeks, ponds, reservoirs, and agiculture ditches where watersnakes have been observed in the state typically also support other non-native aquatic species, such as fishes from the Eastern US (e.g. bluegill, bass) and bullfrogs, which are also not native to California. Watersnakes do not have a stripe down their back. They are generally either a uniform dark color, or have wide blotches, bands, or saddles on their backs. Watersnakes tend to be heavy bodied (wide in the middle). You can see photos of non-native watersnakes here and here at the California Herps website.
|
||||||
Related Content:Watersnake information from California Department of Fish and WildlifeCalifornia Nerodia Watch at iNaturalistPublic information flyer for Northern California: |
PREVIOUS NEWS
May 2016 Trapping for Water Snakes in Yuma, AZ
For general information on invasive water snakes in California, or to report on your observations, please contact: Mike Fuller. |
Purpose of this SiteThe purpose of this web site is to report on the distribution of non-native water snake species in California. Here, you will find information on the location of established populations and new sightings, as well as updates on control measures taken to reduce threats to native fish and wildlife. Natural resource agencies involved include the US Fish and Wildlife Service, US Geological Service, and California Department of Fish and Game.Two species of exotic water snake (genus Nerodia) have become established in California: Confirmed Sightings and Populations (two species):
A third species, the diamond-backed water snake (N. rhombifer), was recorded at the Lafayette Reservoir, east of Berkeley, in the 1990s. That population declined to undetectable levels and may have died out. However, recent reports of water snakes at the Lafayette Reservoir suggest that the diamond-backed water snakes may be recovering at that location. |
Map of Water Snake Sightings |
References Cited
How Did Water Snakes Invade California?For many years, water snakes and other non-native reptiles were routinely imported to California for the pet trade. We believe the source of most water snakes in California is the intended or accidental release of snakes purchased at pet shops. The fact is, water snakes make poor pets. They are prone to biting and spray-defecating with a foul-smelling musk secretion when handled. Water snakes rarely become tame and do not prosper in captivity. Reptile enthusiasts accustomed to more easily handled species can become discouraged with pet water snakes. Not wanting to kill the snakes, owners may simply release them into the closest aquatic habitat. We believe this is a likely reason that water snakes can now be found outside their native range. |
Photos of Non-Native Water Snakes |
Threat Posed by Non-Native Water SnakesWithin North America, snakes in the genus Nerodia are native to the eastern and southeastern US, eastern Canada, and Mexico. Unlike the cottonmouth water moccasin (Agkistrodon piscivorus), which has not become established in California, water snakes are not poisonous and do not present a threat to human safety. Although water snakes are not dangerous to people, as introduced (exotic) predators they pose a threat to natural systems and native species. Water snakes feed primarily on small fish, frogs, tadpoles, and possibly crayfish. Exotic predators can damage native ecosystems by decimating populations of their prey. Exotics also compete with native species for food, and can carry new parasites or diseases which may spread to native species. Many Californian fish, amphibians, and aquatic snakes have become rare and in danger of extinction in California, largely as a result of the loss of natural freshwater habitats (over 90 percent of the original extent of freshwater habitat in California has been lost; US Geological Survey). Already suffering from loss of habitat, native aquaitc organisms now face the added stress of introduced water snakes. |
Similar Native Snake SpeciesSeveral aquatic snake species that are native to California superficially resemble non-native water snakes, and care should be taken not to harm unidentified snakes that appear to be water snakes. Garter snakes (genus Thamnophis) are the native snake species most commonly found in or near fresh water in California. Many garter snakes can be distinguished from water snakes by the central stripe that runs down the back of garter snakes. The stripe may be yellow, orange, red, tan, grey, or white. Water snakes lack the central stripe, and have crossbands or no obvious markings instead. However, two species of California garter snake, the Sierra garter snake and two-striped garter snake, lack the central stripe, and one other species, the Oregon garter snake, sometimes has a stripe, and sometimes does not. Therefore, the latter three species may be more easily confused with non-native water snakes.Native garter snakes found in California include the following:
|
Legal Status of Water Snakes in CaliforniaAs of January 2008, all non-native water snakes (genus Nerodia) are regulated as restricted animals by the California Department of Fish and Game (Sec. 671, Title 14, Calif. Code of Regulations). It is now unlawful to import, transport, or possess water snakes of the genus Nerodia in California without a permit.If you are currently in possession of one or more water snakes of the genus Nerodia, PLEASE DO NOT RELEASE THEM. The snakes should be disposed of humanely, such as with the assistance of a veterinarian. |
More Photos of Water Snakes (with captions)
Click the above text, or photo bar below, to view photos of water snakes captured in California. |
Where to Report Sightings of Water SnakesIf you have photographs of aquatic snakes in California that you believe to be non-native water snake species, you can send them to Mike Fuller for confirmation. Please include the location and date of the photos, as well as the name and contact information of the photographer. |
LINKS
|
General Documents About Invasive Species
|
References Cited, with Notes
Balfour, P. S., and E. W. Stitt. 2002. Geographic distribution: Nerodia fasciata fasciata (banded watersnake).
USA: California: Sacramento Co. Herpetological Review 33:150.
Balfour, P.S., E.W. Stitt, and M.M. Fuller. 2007. Geographic distribution: Nerodia fasciata pictiventris (Florida water snake).
Herpetological Review 38:363. (Provides updated information on populations found in Northern and Southern California).
Fuller, M.M. and B.W. Trevett. 2006. Geographic distribution: Nerodia fasciata pictiventris (Florida water snake).
Herpetological Review 37:363. (First published record for the Florida water snake population in California).
Stitt, E.W., P.S. Balfour, T. Luckau, and T.E. Edwards. 2005. The southern watersnake (Nerodia fasciata) in Folsom, California: history,
population attributes, and relation to other introduced watersnake in North America. Final report to US Fish and Wildlife Service. ECORP Consulting Inc.