The waters around Istanbul have turned a striking shade of turquoise.
A natural phenomenon called a "phytoplankton bloom" has turned the normally dark waters of the Bosporus and the Golden Horn into an opaque tone of light blue. It's caused by microscopic organisms that have inundated the Black Sea just north of Turkey's largest city.
Berat Haznedaroglu, an environmental engineer, says it's a normal annual event.
"This year we got a lot of rain events that carried nutrients from the Saharan desert to the Black Sea, which created an optimal environment for this phytoplankton to bloom," said Haznedaroglu, who works at the Institute of Environmental Sciences at Istanbul's public Bogazici University.
In a statement published with a satellite image of the Black Sea, NASA said the milky coloration is "likely due to the growth of a particular phytoplankton called a coccolithophore."
The microscopic organisms support fish, shellfish and other marine organisms but can also cause die-offs of marine life due to loss of oxygen from the water if the "blooms" are too widespread.
The Bosporus, a strait that separates Europe from Asia, also connects the Black Sea to the Sea of Marmara and is a heavily used waterway.