Turkey on Tuesday pledged to save the Sea of Marmara with a disaster management programme to clean up a slimy "sea snot" outbreak threatening marine life and the fishing industry.
The thick layer of organic matter, also known as marine mucilage, has spread through the sea south of Istanbul covering harbours, shorelines and great areas of the surface.
Some of it has sunk below the waves, suffocating seabed life.
Turkish Environment Minister Murat Kurum said a total of surface-cleaning boats and those that install barriers, as well as 18 other vessels, were working to prevent the spread of the mucilage.
Illegal fishing and "ghost" nets would be banned and Turkey would declare Marmara a protected area by the end of 2021, Mr Kurum said.
"We are starting our cleaning efforts both on land and at sea at 15 points today," he said.
"We are determined to save the Marmara and we will save it."
About 1,000 workers would bring the waste to shore and take it to municipal centres, Mr Kurum said.
Scientists say climate change and pollution have contributed to the proliferation of the mucilage, which contains a wide variety of micro-organisms and can flourish when nutrient-rich sewage flows into seawater.
Residents welcomed the clean-up but complained about what they called years of uncontrolled pollution in the sea.
"Of course, this sea snot is something that is caused over a few years," said Kadir Saydam, 65, a pharmacist.
"Formed by our years-long unawareness, the harmful substances thrown into the sea caused a vomiting in the seabed and when there was no current, it stayed there.
"Having the cleaning efforts is good visually."
President Recep Tayyip Erdogan has blamed the mucilage on untreated water from cities including Istanbul, home to about 16 million people, and pledged to "clear our seas from the scourge".