Rare Green Sea Turtle Spotted Far From Home In California's San Joaquin River [VIDEO]

An Eastern Pacific green sea turtle was recently spotted swimming far from home in Northern California's San Joaquin River. While the rare sea turtles are often found in waters near Mexico, this one may have been lured north by warmer El Niño waters, and researchers are concerned more will follow.

Green turtles (Chelonia mydas) are the largest of all hard-shelled sea turtles and are unique in that they are strictly herbivorous, feeding primarily on seagrasses and algae. Green turtles are typically found in one of three tropical or subtropical habitats: beaches for nesting, open ocean, or coastal areas.

"When I first saw it, I thought it was a plastic bag," Dan Maloon, a local fisherman, told CBS Sacramento.

Researchers from the Turtle Island Restoration Network in Marin County later were able to confirm the turtle was in fact an Eastern Pacific green sea turtle – a relatively rare species with only a few thousand known individuals left in the world.

"This animal clearly came from the Pacific Ocean, there's no question about that," spokesman Todd Steiner said. "Apparently went north into San Francisco Bay and now it seems to be heading directly east." (Scroll to read more...)

Regardless of how the animal ended up farther north, researchers are concerned that the endangered animals could become "cold stunned," a hypothermic reaction that involves decreased heart rate and circulation, as well as lethargy, shock, pneumonia and possibly death from colder northern waters. Sea turtles are cold-blooded reptiles and depend on external sources of heat.

"If it gets too cold, it basically becomes hypothermic and can no longer function," Steiner added.

While the recent finding is quite unusual, a small group of 30 to 60 green sea turtles has also been seen in the San Diego Bay. This turtle population often migrates from Mexico to northern waters in order to forage in the Bay's eelgrass beds. 

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