Turkey's environment minister pledged on Sunday to defeat a plague of "sea snot" threatening the Sea of Marmara with a disaster management plan he said would secure its future.

A thick slimy layer of the organic matter, known as marine mucilage, has spread through the sea south of Istanbul, posing a threat to marine life and the fishing industry.

Harbours, shorelines and swathes of seawater have been blanketed by the viscous, greyish substance, some of which has also sunk below the waves, suffocating life on the seabed.

Environment Minister Murat Kurum said Turkey planned to designate the entire Sea of Marmara a protected area, reduce pollution and improve treatment of waste water from coastal cities and ships which has helped the sea snot to spread.