I saw the green turtle (Chelonia mydas) twice. The first time I saw one I was heading back to shore at Paradise Beach, Coral Bay, cold and hungry after two hours in the water. The second time I saw one I was snorkeling in The Lagoon, a snorkeling spot which is accessible by only 4WD or quad trek bike.
The turtle I saw had a carapace (shell) consisting of five central scutes (bony plates)(A-E) flanked by four scutes on each side (1-4). This characteristic fits the Wikipedia description of a green turtle. I just couldn't see the turtle's snout and its underside, so I couldn't confirm its identity further. But the colors of the carapace also suggest that it's a green turtle.
It was exciting to bump into it because it was an unexpected encounter. The water was only about 3 m deep where I found the turtle and I was probably just 30 m from shore.
The green turtle gets its name because its fat is green and is more evident when the animal is boiled up into soup ("The Marine Life of Ningaloo Marine Park & Coral Bay" by Ann Storrie & Sue Morrison, 1998).
The Shark Bay World Heritage website says this:
"... the species actually gets its name from the colour of its fat. People know what green turtle fat looks like because the turtle was hunted in Australia for its eggs and meat – which was boiled into soup – until it was given legal protection in 1973."
And the animal's green body fat is believed to be due to consumption of lots of seagrass and algae (Ref).
I was swimming above it for a while, maybe a minute or two.
The turtle in this clip was the one I saw on my way back to the shore. It swam to the surface for air and dived down again. It used mainly its front flippers and the back flippers hardly moved at all.
The turtle in this clip was the one I saw in The Lagoon. When I first saw it, it was grazing on some seaweed or seagrass on the sea floor. In the second half of the clip, you can see a fish that kept tagging along with the turtle.