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How Istanbul's Bosphorus Strait is turning from blue to turquoise

NASA said the milky colour is likely due to the growth of a particular phytoplankton called a coccolithophore.

Bosphorus Strait turns turquise blue

A sudden change in the colour of the Bosphorus Strait that divides the continents of Europe and Asia in Turkey's largest city Istanbul since the weekend has alarmed some residents.

Some took to social media to express fears that there had been a pollution spill while others even suggested it could be linked to an earthquake that rocked the Aegean region on Monday afternoon.

Bosphorus Strait

It is a natural strait connecting the Black Sea to the Sea of Marmara, thus being a very strategic waterway. It's length is 32 kilometers (20 miles) in the north to south direction. Bosphorus strait separates the European part from the Asian part of Istanbul. The surface current flows always from north to south; however, a strong countercurrent under the surface creates swirls and eddies.

Scientists give reassurance

Scientists said there was no mystery behind the colour change and the accompanying sharper smell.

Ahmet Cemal Saydam, professor of environmental science at Hacettepe University, told the Dogan news agency that the cause was a surge in numbers of the micro-organism Emiliania huxleyi, also known as Ehux.

"This has nothing to do with pollution," he said, adding it was particularly good for the numbers of anchovies, a popular supper in Istanbul. Across the Black Sea there is an explosion of Emiliania huxleyi. This is a blessing for the Black Sea."

NASA captured the first pictures on May 29

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite first captured the phytoplankton bloom in the Black Sea on May 29.

NASA said the milky colouration is "likely due to the growth of a particular phytoplankton called a coccolithophore". Emiliania huxleyi is a species of coccolithophore.

Emiliania huxleyi

One of the most successful life-forms on the planet, Emiliania huxleyi is a single-celled organism visible only under a microscope. Its astonishing adaptability enables it to thrive in waters from the equator to the sub-Arctic.

Phytoplankton consists of floating, microscopic organisms that make their own food from sunlight and dissolved nutrients. Ample water flow from rivers like the Danube and Dnieper carry nutrients to the Black Sea.

In general, phytoplankton can support fish, shellfish and other marine organisms. Large, frequent blooms can lead to eutrophication the loss of oxygen from water and end up suffocating marine life.