Green sea turtles thrive in the murky and warm San Gabriel river in Los Angeles

When scientists confirmed their existence in the San Gabriel river in 2008 within the Los Angeles metropolitan area, the green sea turtles were thought to be oddballs or lost wanderers.

The federally endangered species usually is found in tropical haunts amid coral reefs or on the sandy beaches where they lay eggs. But this colony was cavorting in the southern end of the river, where the flood control channel’s tainted urban run-off mixes with tidal flows in the shadows of electric power plants and the 405 Freeway.

With each massive turtle that poked its grapefruit-size head above the murky water for a gulp of air came questions.

How many were there? What were they eating? Were they adapting to the challenges the two-mile-long, 100-yard-wide channel between the cities of Long Beach and Seal Beach presented: fishing hooks, motorboats, illegal dumping and tonnes of garbage that washes in every time it rains?

After years of monitoring their behaviour and tracking their movements, federal scientists assisted by a small army of volunteers organised by the Aquarium of the Pacific and the Los Cerritos Wetlands Authority are coming up with answers to some of the riddles the turtles pose.

“The green sea turtles in the San Gabriel River are thriving,” said Dan Lawson, a biologist with the National Marine Fisheries Service. “Over the past decade, we’ve seen about 100 of them in the river and in nearby Alamitos Bay, Anaheim Bay, Huntington Harbour and the Naval Weapons Station.