A mucus-like substance has blanketed parts of the Marmara Sea near its coasts over the past few months. It is not an unprecedented occurrence and is tied to microorganisms as well as to a type of substance occasionally produced by phytoplankton. But it is larger and more ubiquitous than ever this year. The viscous substance is a challenge for marine life, particularly the fish, and scares away swimmers as the summer slowly sets in the region.

Local authorities initiated a clean-up recently, with cleaning boats sweeping vast stretches of water near the shore but wiping away the snot in the open sea remains an insurmountable problem.

The phenomenon is linked to high sea temperatures stemming from climate change that has made itself more evident in the country in recent years, as well as the discharge of untreated sewage and other pollutants to the sea. Experts say apart from cleaning, there is little that can be done other than waiting for the substance to disappear itself, as seen in some parts of the Marmara.

"The sea was in a shroud and left to die," Yaprak Fidancı, an activist who spoke on behalf of local nongovernmental organizations (NGOs) at an event on the issue in Kocaeli province, said Thursday. Fidancı said sea snot seriously hurt the fishing industry by damaging nets, and in some cases, fishing boats. "They are unable to fish and the fishing season that ended early this year may not even begin next year," she said. Fidancı said the Marmara Sea and the Gulf of Izmit where Kocaeli is located have been home to rich flora and fauna but pollution "broke" the food chain in the sea. Some 150 tons of sea snot were collected in 50 days from the Gulf of Izmit by local municipality’s cleaning boats. The substance is disposed of at the municipality’s waste treatment facilities.

As a matter of fact, mucilage is damaging the livelihoods of fishermen as the lack of fish – which sometimes turn up dead atop the viscous substance – drove up fish prices. Fishermen operating small boats are particularly at risk. Ibrahim Pehlivanoğlu, who heads a cooperative of fishermen in Süleymanpaşa, a coastal town in northwestern Tekirdağ province whose coast was covered with snot, says fishing became impossible for locals. "Without more fish, we have to sell what we have for a higher price and the demand is shrinking in turn. Fishermen are the main victims of sea snot. It disappeared in some places but remains elsewhere and it does not look like it will go away," he told Anadolu Agency (AA) on Wednesday.

Along with cleaning, wind can help to get rid of the snot, as is the case off the coast of Çınarcık, a town in Yalova province, south of Istanbul. Mucilage is less dense after weeks on the surface, though it appears to linger below the surface.

Nevertheless, it may have long-term effects for the fish, as experts say it damages breeding grounds and blocks migration paths. Indeed, it is more dangerous underwater than on the surface, as it sucks out oxygen vital for species. Another danger is its impact on photosynthesis, which involves utilizing sunlight for survival and growth. Although fish caught in snot are edible, it may still pose a health risk, experts say, pointing out that it creates a suitable environment for bacteria growth, including the growth of E.coli. Toxic organisms swept by the snot, when attached to fish, also creates a risk.

The southern coasts of the Marmara Sea are also in danger of losing tourism revenue. A vast area stretching from Balıkesir to Yalova is a popular destination for Turkish vacationers and home to summer residences for thousands of people hailing from big cities, including Istanbul. "No one comes because they cannot swim here," Ramazan Uğurlu, a Çınarcık resident, says. "I have been living here for years but I have never seen anything like this," he told Demirören News Agency (DHA).

For a while, sea snot has been exclusive to Marmara but Özgür Baytut, a hydrobiology associate professor at Ondokuz Mayıs University, said the thick layer that emerged at the main port of Black Sea province Samsun recently has been confirmed as marine mucilage. Baytut says cleaning is the only option for now, but it is difficult when the snot is further away from the coast. "We will have to wait and stop any pollutants from harming the sea," he told Ihlas News Agency (IHA).

Baytut said sea snot has been a common occurrence for centuries and has been reported in the Mediterranean since the 18th century. "It was common in Italy back then. Since the early 2000s, it has been reported, although on a smaller scale, in the Marmara Sea. There were reports of sea snot as well in the Black Sea two decades ago. But it is truly unnatural to see such dense mucilage covering a larger area," Baytut said. He pointed out that the spring temperatures support the snot's growth, especially in tranquil seas, and it may continue well into mid-June. Baytut said pollution has made the snot more visible.

In Istanbul, the snot reached as far as Kurbağalıdere, a creek straddling the seaside districts of the city’s Asian side, while the city’s main harbors have been taken over by the mucilage. Istanbul municipality said the snot will "go away" in a month or two. In a statement earlier this month, Istanbul Metropolitan Municipality (IBB) said the mucilage was a quite common, seasonal biological process, especially in seas like the Marmara. "Currents, temperature and the salt rate at sea are factors in the emergence of mucilage. The mucilage may disappear when the seawater is warmer and temperatures go back to the seasonal normal," the statement said. The IBB said the examination of samples from the sea showed the process was not creating any pollution and does not contain any hydrocarbon waste.

Mustafa Sarı, dean of Bandırma Onyedi Eylül University's Maritime Faculty, attributes the phenomenon to pollution.

"The increase in the number of elements such as nitrogen and phosphorus in the sea is largely related to domestic waste such as sewage. Domestic waste released into the sea without treatment increases the nitrogen and phosphorus load of the seawater. The sea snot resulting from this excessive proliferation is generally seen from 5 meters (16 feet) to a depth of 25-30 meters," he told Anadolu Agency (AA) last month.

"The first expected situation for sea snot is to settle to the bottom of the sea. After the sea snot coats the seafloor, it ends all life in the sea. In the absence of oxygen, a huge number of deaths take place on the seabed. At the same time, sea snot clogs the gills of the fish and causes drowning. However, this trend is global. As the effect of warming increases, some special groups of toxic microorganisms will emerge together with sea snot. These toxic substances affect some fish more and others," Muharrem Balcı, a lecturer on hydrobiology at Istanbul University, told a Demirören News Agency (DHA) reporter.

Climate change that affects the country, which experienced a milder winter than usual this year after one of the worst years for weather-related disasters, still weighs heavier than pollution for the phenomenon. Phytoplankton, which thrives in warmer waters, is among the actors of the mucilage in the Marmara, where temperatures were several degrees higher than average. Seawater temperatures already dealt a blow to fishermen looking for hamsi, a type of Turkish anchovy, and the sea snot may be the next disaster – though they are not without blame too. Some experts link overfishing to the unbridled growth of phytoplankton, thanks to the absence of natural predators.