The Press-Telegram has an article about green sea turtles (Chelonia mydas) in Long Beach!
Apparently, about a dozen of the endangered critters are swimming up the San Gabriel river, attracted by the warmth from the powerplant that uses the river to cool its generators.
Read the article here.
Presumably, the turtles are hanging out in the soft-bottomed estuarine portion of the river (south of PCH), and not going into the concrete-lined freshwater portions (pictured below):
I have never seen turtles in the San Gabriel River, but now that I know they are there, I'll be sure to look!