Green sea turtles typically live in the tropical waters of places like Mexico or Hawaii, so it comes as a surprise to scientists to find a group swimming year round in the San Gabriel River in Long Beach.
These turtles are believed to be the northernmost population of foraging green turtles, 100 miles further up the coast than the next closest cluster in San Diego.
Researchers are eager find out what’s keeping them in this unlikely urban location.
"This is not a tropical paradise or the other things that usually come to mind when you think about sea turtles," said Dan Lawson, a researcher with the National Oceanic and Atmospheric Administration.
Lawson, who studies these animals, pointed out that the three miles stretch of river where turtles have been spotted is often mired with trash. It is next to a busy road and a military base.
Still, it has a few things making it a good home for sea turtles.
For starters, the river is a mix of salt and fresh water, which is good for sea turtles, and it seems to have plenty of food.
It's also between two power plants.
While most of us wouldn't want these noisy neighbors, the plants actually seem to be helping the turtles.
That's because they both suck in cold ocean water and use it to cool their generating systems. This process ends up heating the water, which is then dumped in the river.
The result is a warm outflow that acts like a sort of turtle Jacuzzi.
(This map shows where the turtles like to swim. Just north of Westminster Road there are two power plants that expel warm water into the river.)
"It’s certainly creating a unique environment that is beneficial for them," said Lawson.
But there’s a catch. Over the next decade or so, the plants will phase out this method of using ocean water as a cooling mechanism.
That means, eventually, there will be no more warm water in the river for the turtles..
Lawson said it’s unclear how this will effect this federally protected species, but as of now, NOAA has no plans to intervene on their behalf.
He thinks the cooler water will likely slow their bodies down, but the warmth might not be the only reason they’re here.
Cal State Long Beach researcher Dan Crear has tagged some turtles with tracking devices and found they don’t just stick to the warm parts of the river.
"It can vary quite a bit depending on the season and depending on the turtle," he explained. "I’ve detected them outside of the river within Alamitos Bay Marina at the mouth of the river, and then also in Anaheim Bay harbor."
This leads him to believe that maybe these turtles aren't totally dependent on the warm outflows.
He also pointed out that there are other power plants pumping out warm water in the area, but only this one has turtles.
Still, both Crear and Lawson agree that it'll be important to watch what happens to this population as the warm water disappears.
Casandra Davis helps train new volunteers. She says you can often tell the size of a turtle by looking at its head as it surfaces.
"The small turtles have heads about the size of a golf ball and the large turtles, their heads are about the size of a soft ball or a grapefruit," she said.
As for their bodies, smaller turtles can be the size of a clipboard while larger ones can be the size of a school desk.
The group has been carrying out this sea turtle census for the past three years. They come once a month to the same stretch of river and count turtles.
Davis estimates there are more than 30 turtles in area. Volunteer Peggy Morrison insists one time she saw 40 in a single day: "It was amazing, the miracle turtle-sighting day!"
The data these citizen scientists gather will help establish a baseline number for this population. Then researchers will know if and when the number of turtles starts to drop.
Still, these turtles have more than just the temperature of the river to worry about.
Speeding boats can strike them as they surface. Fisherman can accidentally hook them, and sometimes they get tangled up in trash.
That happened on a recent visit to the river. Volunteers spotted a medium-sized turtles struggling to swim near the riverbank.
Dan Lawson pulled it from the water and found it was tangled in a mess of fishing line and rope.
Using a small knife, he was able to free it and place it back in the water. But it's a reminder that this population still needs protecting.
"The outlook I think it promising," Lawson said afterward.
"We’ve got a community here that’s gotten really interested in [the turtles], I know they are going to do what they can to look out for the turtles so everything seems to be pointing in the right direction."
In fact, he thinks the fact that this population has taken hold in such an unusual spot might be evidence that decades of sea turtle conservation are paying off.