Southern Watersnake - Nerodia fasciata

The species occurs naturally in the southeastern United States, from North Carolina to Florida, up the Mississippi into southern Illinois and east into central Texas.


Introduced Established Populations in California

The Southern Watersnake has been established in at least three locations in California.


1 - Established in and around Lake Natoma in the city of Folsom, Sacramento County
(Peter S. Balfour, Eric W. Stitt, Michael M. Fuller and Tara K. Luckau. Herpetological Review 38(4), 2007),

2 - Established at Machado Lake (aka Harbor Park Lake) in Harbor City, Los Angeles County.
Identified as Nerodia fasciata pictiventris - Florida Watersnake.
(Michael M. Fuller and Bryce W. Trevett. Herpetological Review 37(3), 2006)

Biologists from the USGS and CDFW with authorization from the LA Dept. of Parks and Recreation have made efforts to eradicate Nerodia from the lake. In 2010 approximately 300 Florida watersnakes were trapped and removed. Necropsies on the snakes performed by biologists with the USGS, the US Fish and Wildlife Service, and UC Davis, found no remains of native species in their digestive tracts. Instead, the watersnakes were found to prey mostly on other invasive species found in the lake. According to USGS snake ecologist Robert Reed, young snakes prey mostly on nonnative mosquito fish, while older snakes prey on bullfrogs, and bullfrog tadpoles. The ongoing effort to clean up the lake and improve the water quality will increase the food source for the snakes and won't reduce their number. Reed says that the lake would have to be drained for at least a year in order to get rid of the source of food for the watersnakes, which would be the only sure way to get rid of the snakes.

LA Times 6/11/16


3 - In October 2015 state biologists confirmed the presence of southern water snake (Nerodia fasciata) northeast of Yuma Arizona along the Colorado River at the border of California and Arizona at Laguna Dam, Senator's Wash, and at Mittry Lake in Arizona.
(J. Clayton Sharp, Herpetological Review 49(3), June, 2018.)

A U.S.F.W.S. article, Battling the Invasion of Watersnakes, mentions the possibility that equipment traveling from a military base in the southeastern U.S. to a U.S. Army base near where the snakes have been found could be the source of the watersnake introduction, but Clay Sharp, who discovered the Nerodia in the Yuma Basin, told me that he has never seen any Army vehicles or equipment in the area where he has captured the snakes but he did see a Dredge from Florida and working tanker trucks from Louisiana doing restoration work in the Multi-Species Conservation Project area and he thinks that could be the source of the introduction. While snakes have been known to hitch a ride on military planes and vehicles (the Brown Tree Snake was accidentally transported to Guam either in ship cargo or by being transported on aircraft, probably hidden in the landing gear) I think it's most likely that somebody simply dumped some unwanted pet snakes in the area.

The California Nerodia Website reports on news, publications, and sightings related to non-native Nerodia species in California.

California Nerodia Watch enlists reports of wild Nerodia found in California.

California Department of Fish and Wildlife

The Southern Watersnake (Nerodia fasciata) in Folsolm California (PDF)

Gibbons, J. Whitfield, Michael E. Dorcas. North American Watersnakes - A Natural History. University of Oklahoma Press. 2004.

Balfour, P. S., and E. W. Stitt. Geographic distribution: Nerodia fasciata fasciata. Herpetological Review 33:150 2002.

Peter S. Balfour, Eric W. Stitt, Michael M. Fuller and Tara K. Luckau. Herpetological Review 38(4), 2007

J. Clayton Sharp, Herpetological Review 49(3), June, 2018

Michael M. Fuller and Bryce W. Trevett. Herpetological Review 37(3), 2006

Robert Powell, Roger Conant, and Joseph T. Collins. Peterson Field Guide to Reptiles and Amphibians of Eastern and Central North America. Fourth Edition. Houghton Mifflin Harcourt, 2016.

Conant, Roger, and Joseph T. Collins. A Field Guide to Reptiles and Amphibians Eastern and Central North America. Third Edition, Houghton Mifflin Company, 1998.

Bartlett, R.D., & Alan Tennant. Snakes of North America - Eastern and Central Regions. Gulf Publishing Co., 2000.