Underwater visibility, sometimes greater than 30meters, and the white sand sea floor work together to paint the Okinawan waters a deep azure blue.

水下能见度有时可以超过30米，加上白色的海底沙石的装扮，更突出了。

youdao

Underwater visibility in the Foyle is very poor at the best of times making identification difficult.

BBC: Experts to examine River Foyle, Derry, wreck

Even when the sharks are found closer to the ocean surface, they spend their time in the cool-temperature, plankton-rich waters that limit underwater visibility and make diving difficult.

CNN: Scientists discover winter home of world's second-biggest fish

"The visibility underwater is amazing, " says Paul Irvine of Dehouche.

FORBES: Fernando do Noronha - Brazil