Water snakes, common in the Eastern United States, have been discovered moving into California waterways amid fears they'll threaten endangered native species, experts say.

Around 300 snakes from two species -- the southern water snake and the common water snake -- were found around the region of the state capitol Sacramento and around 150 have been spotted in Long Beach in Southern California, researchers at the University of California, Davis, say.

The most likely source of the "invasion" is people releasing pet snakes into wild environments, they say.

The common water snake it particular is found throughout the Eastern U.S. but has rarely been observed west of the Rocky Mountains -- until now.

The researchers expressed concern that potential California habitats where the invasive snakes could get a foothold are also home habitats to native species like the California tiger salamander and the giant garter snake.

Although not venomous, water snakes could prey on native amphibians, fish and even other reptiles.

And even if they don't become prey, many California species could face pressure from the invasive species in competition for food.

The garter snake, in particular, would find itself in direct competition for the same food sources, the researchers said.

"Water snakes are not picky eaters," study co-author Brian Todd, a conservation biologist in the university's Department of Wildlife, Fish and Conservation Biology, says. "With their predatory nature and generalist diets, our already imperiled native fish, amphibians and reptiles have much to lose should introduced water snakes become more widespread."

The common water snake could move from California into Oregon and central Washington, the researchers say.

In addition, they say the two invasive species are capable of interbreeding, which could result in hybrids capable of tolerating a wider range of climates and expanding their potential invasive range.

Todd said the study was an attempt to aid state wildlife officials in getting a head start on eradicating the two invasive species before they move into more areas and do more harm.

"So what we did was try to get out on front of an issue and get some idea of the risk posed by these non-native species to other native species in California with the hope that that could guide management for the removal or eradication of these non-native species," he said.

If no action is taken quickly that will just increase the future economic and ecological costs of controlling the snakes, he said.