My first sight of it came one morning in June, as I rode the ferry through the Bosporus strait: a toxic glint on the sea’s surface. I initially thought it was oil, spilled from one of the many large container ships that pass through Istanbul via the Bosporus. Yet as we neared the glint, a sallow sludge marbled the water around the boat. In some areas, it was as thick and buoyant as fiberglass insulation. Its surface, coated with foamy bubbles and viscous puddles, was littered with balloons, bread crusts, and Styrofoam food containers.
It’s called marine mucilage, but the world knows it better as “sea snot,” thanks to the tsunami of stories that went viral when it overtook the Sea of Marmara in May. The internet marveled at the mess and moved on, but here in Istanbul, the sea snot hijacked the summer. Its unearthly, unavoidable presence closed down beaches and dominated conversations. For some of us, it was more profoundly unsettling.
This isn’t what I imagined global warming would look like. I was braced for bigger wildfires and rising seas; I wasn’t ready for sea snot. If the story of the Sea of Marmara in the summer of 2021 is a preview of what’s to come, the effects of climate change will be not only terrifyingly destructive but also weird, uncomfortable, and unbearably gross.
The Marmara is a historic inland sea that connects the Black Sea with the Aegean via the Bosporus and Dardanelles straits. Along its shores, which are rimmed with ports, piers, summer houses, and factories, fishermen in wooden boats still haul in sea bass, mullet, and anchovies. But over the past decade, marine species such as bluefin tuna and swordfish have gone commercially extinct, populations of many other fish species have declined, and jellyfish have mobbed the coastline, all symptoms of an ailing ecosystem. The mean surface temperature of the Marmara, like that of many seas, is rising due to climate change, but the Marmara’s has increased by 2.5 degrees Celsius—1.5 degrees more than the global average, making it a leading indicator for seas around the world.
This intense warming, along with decades of abuse from pollution and overfishing, sent the Marmara into a state of maritime shock. At the end of 2020, increased concentrations of phosphorus and nitrogen led to a boom in phytoplankton, single-celled organisms whose name means “plant drifter” in Greek. The Marmara’s warming surface temperature also caused its waters to stratify, slowing the currents that would normally help disrupt algae growth.
Eventually, the phytoplankton began to run out of nutrients, causing the cells of some species to exude a sticky substance. As these cells died, they collided and stuck together, aggregating into globs that hovered in the warmest layer of the stratified water. With time and exposure, the globs turned into a submerged mat of mucus that trapped nearly everything around it—bacteria, fish larvae, dead cells, debris. Bacteria thrived on the dead phytoplankton, adding to the mat’s mass. “At that point, it takes on a life of its own,” Mustafa Yucel, a marine-science professor at Middle East Technical University’s Institute of Marine Science, told me. With increasing water temperatures, he said, we should prepare to see more extreme reactions in our seas—including invasive-species outbreaks and massive algal and seaweed blooms.
The fisherman Roy Oksen, the chief of one of Istanbul’s fishing cooperatives, remembers the first time he couldn’t pull his fishing net into his boat. Something was weighing it down. He asked a shipmate for help, and together they hoisted the net out of the water. Instead of fish, it was full of a dark, slippery goo. Soon, he told me, the mucilage was clogging not only nets but also boat motors.
I met Oksen at his fishing co-op’s headquarters, a harborside hut where we sipped tea surrounded by coiled ropes and the smell of bait and petrol. The window, which usually provided a view of the water, was plastered with flyers stating that seafood from the Marmara was safe to eat despite the mucilage. Oksen explained that a fish that would have sold for 50 lira before the sea-snot outbreak would now sell for just 10, even as he was working harder to catch fewer of them. To make matters worse, news of the outbreak had led to a 70 percent drop in fish sales in cities around the Marmara. The equipment problems ultimately got so bad that Oksen and other fishermen were forced to end their season early. “If this continues this year or next year, I’ll have to go look for a new kind of job to survive,” he said.
As the mucilage drifted below the surface, it started to rot, beginning a nasty metamorphosis. The decay was spurred by viruses and bacteria that multiplied in the mucus and ruptured the dead phytoplankton cells, causing them to release more mucus and gas. As the gas inflated the mucilage, it began to rise. In May, it broke the surface of the Marmara, making its grand entrance into the public eye. It pooled in the shallow bays near Gebze, haunted the harbors around Erdek, and flourished on the shores of Istanbul’s tony Princes’ Islands. Kadıköy smelled like rotten eggs. Headlines about the sea-snot outbreak went viral, and the world recoiled in disgust.
In early June, I went to Kadıköy, a trendy neighborhood on the Asian side of Istanbul that had been hit hard by the outbreak. Some of the mucilage mats were as thick and dense as a ’70s shag rug; others were light and frothy, like a frappuccino. On a normal summer day at the Kalamiş Marina, one of Turkey’s poshest, yachts glide in and out of their slips, whisking people to the Princes’ Islands or on a sunset cruise. When mucilage arrived at the marina, staff laid an orange oil-spill boom in the water in an attempt to hold it off. But it quickly overcame the boom, and soon the marina’s waters were carpeted with mucilage. Yachts were imprisoned in sea snot. Swarms of flies clustered around the mucilage, menacing the sailors. People no longer wanted to be near the water, Nail Baktır, who runs a sailing school in the marina, told me. As he stood on the deck of his docked boat, he pointed to the scum rimming its hull. When he first saw the mucilage, he thought that the masses were the corpses of microorganisms from deep within the sea. “We’re done. The Marmara Sea is over. The bodies are floating.” His blunt conclusion: “We killed the Marmara.”
As Baktır alternated between gripping the boat’s wheel and stroking his long captain’s beard, he said that although he had spent his whole life in Istanbul, the mucilage was making him consider a move to southern Turkey, where the water is cleaner. Maybe, he said, his grandchildren will see the Marmara the way it was when he was a child—if environmental concerns are taken more seriously in the future.
Meanwhile, the bacteria in the mucilage degraded, releasing enough gas to inflate small surface bubbles, ballooning the mucilage into conglomerates that scientists call “clouds.” With the clouds acting as sails, Turkey’s fierce westerly lodos pushed the mucilage around the Marmara. Some flocs—as loosely clumped masses of mucilage are called—sailed all the way to Greece, raising concerns about the international spread of bacteria and viruses (none of my sources was aware of any reports of illness directly attributed to the mucilage).
As I left the marina, I passed a team of municipal workers wearing life vests over Aegean-blue shirts, spooning the sea snot out of the water with what looked like pool skimmers. Scoop by scoop, they ladled globs of mucilage into garbage bags, then tied the bags and tossed them into a truck bound for an incineration center.
Elsewhere on the Kadıköy seafront, more oil-spill booms temporarily corralled the mucilage so that it could be siphoned up by trucks with high-suction vacuums. Municipal cleaning boats puttered through the water, collecting solidified mucilage with the help of conveyor belts meant for clearing litter. The efforts seemed well intentioned but Sisyphean; the phenomenon was unprecedented, and the infrastructure to handle it nonexistent.
For more than a century, the Princes’ Islands have served Istanbul’s bourgeois as a refuge from the pollution and other unpleasantries of the megalopolis. People navigate the car-free archipelago by foot or carriage, passing neoclassical vacation homes old enough to have housed the likes of Leon Trotsky. Yet on a cloudless, 80-degree day in July, the islands’ beaches sat empty. In one cove, lounge chairs stood in neat, colorful rows, but no one lay in them. The sand was unmarked by footprints. Just offshore, mucilage swirled like the contents of a witch’s cauldron. According to Ayşen Erdinçler, an environmental-science professor at Boğaziçi University and the head of Istanbul’s Department of Environmental Protection and Development, the risk of contracting a bacteria-borne illness from swimming increases 12 to 18 times when concentrated mucilage is present.
As in Kadıköy, municipal vessels chugged through the snot, endeavoring to suck it up with industrial hoses. Pedestrians paused and glared at the scene, brows furrowed. Tourists scurried by with masks on their faces and cameras around their necks. One woman tsk-ed; another covered her mouth and nose, disgusted by the sight or smell or both. This time it wasn’t the mucilage itself that struck me—desensitization had kicked in—but the surreality of a summer without swimming. Our summer had become a René Magritte painting, a collision of ordinary objects producing an unfamiliar whole. “Everything we see hides another thing,” Magritte once said, and as I watched the mucus curdle in the water, I wondered what else it veiled.
Some people stood at the water’s edge in their swim trunks, either debating their options or persisting in denial. Some beach-club owners, desperate to put patrons at ease, baptized themselves in the now-umber water, reemerging with proclamations such as “See, nothing happened to me! I’m fine!” Whether or not this demonstration reassured people of the water’s safety, they wearied of the heat, and soon they were creeping back to the shoreline.
One miserably hot and humid Saturday, I sat on the edge of a dock in the islands, contemplating my first swim since the outbreak had begun. It was Turkey’s second-hottest July on record since 1971, and the prospect of swimming in the sea was seductive. Besides, the mucilage was no longer floating in chunky continents, as it had in June; it had become lighter and creamier, the shade of a café au lait. I had swum in murky waters before, I told myself—in stagnant Sierra lakes at summer camp, and in the bogs of the Mekong River. I watched some friends lower themselves into the water nearby, cooling their bodies while straining their necks to keep their heads well above the water. But as a little blob of mucilage circled my feet, my stomach churned and my body froze. The pleasures of the sea were still just out of reach.
Longing to reunite with the water, I remembered a scene in Orhan Pamuk’s novel The Museum of Innocence in which a character backstrokes in the Marmara to cure his lovesickness. What’s lost when we lose touch with our environment—when a place we turn to for solace or enjoyment is suddenly inaccessible? I knew that the Nobel Prize–winning author, like his character, is an avid swimmer, so I called him to ask how he had been affected by the outbreak.
“When I swim, I am a better thinker, that’s for sure, and also my psychology changes—it gives me some kind of self-confidence,” he told me. “Swimming takes me from a relatively depressive mood to a relatively creative mood.” He went on to observe that this summer, swimming was the new smoking—people avoided the mucilage as if it were carcinogenic. “People are so psychologically scared of this ugly mucilage,” he said. He imagined them on their balconies, watching him swim: “It is the serious novelist Orhan Pamuk!”
Like many environmental disasters, the mucilage outbreak was the sudden consequence of several long-term trends. To better understand them, I took a train from Istanbul two hours east to the Gulf of İzmit. Behind a manicured waterfront of willow trees and park benches, a defunct paper factory testifies to the area’s industrial roots: A century ago, some of Turkey’s first factories produced military uniforms and fezzes here. Today, the gulf remains the industrial heart of Turkey. Ford and Goodyear operate factories here, as do many chemical and fertilizer plants, all making use of the five ports and 35 industrial docks.
Hakan Osanmaz, an environmental-inspection seaplane pilot based in the gulf, had promised to give me a new perspective on the Marmara. We sat in a stuffy prefab office by a dock, lined with photos from Osanmaz’s years jetting tourists around the Mediterranean coast. He wore a tie-dyed Nirvana T-shirt, and he ruminated on the changes he’d seen in the Marmara during his 15 years of bird’s-eye views. The water was once so blue that “it used to look like the Maldives here,” he told me. “It’s kind of like the sea is throwing up. It’s a catastrophe.”
Usually, Osanmaz’s job is to document illegal waste dumping for the local municipality, but since the outbreak, it’s also meant organizing a WhatsApp group to orchestrate the municipality’s mucilage-cleanup efforts.
The sky offers a different perspective on the outbreak. From Osanmaz’s plane, I could see how monstrous Istanbul had grown. Over the past 50 years, the city has spread east along the Marmara, filling its coast with tract homes and high-rise condos, five-star hotels and office complexes. Twenty-five million people, along with half of Turkey’s industry, inhabit the area around the Marmara, and their waste adds to the sea’s burden. Meanwhile, dozens of rivers and streams carry waste into the Marmara. Some of the pollution comes from as far away as Western Europe via the Danube, which empties into the Black Sea and then flows into the Marmara. Osanmaz regularly documents illegal dumping of sewage by international ships passing through the sea.
The ways in which wastewater is treated, it turns out, play an important role in preventing mucilage outbreaks. “Among the sources of marine pollution, 53% of the water coming to the Marmara Basin is discharged into the sea with only pre-treatment, that is to say by discharging the waste water in the houses only by passing it through sand filters and precipitation,” Ayşen Erdinçler, the environmental-science professor, later told me in an email. Advanced water-treatment plants, she said, would remove more of the phosphorus and nitrogen that make mucilage outbreaks more likely, and would also allow the water to reoxygenate. As part of the Marmara Sea Action Plan, established by the Turkish government in response to the outbreak, existing wastewater-treatment plants are being upgraded and new ones are expected to be built within three years.
One day in July, the mucilage suddenly disappeared. Istanbul woke to a sparkling sea. People flooded the shoreline, convinced that the nightmare was over. I called Alice Alldredge, an emeritus marine-biology professor at UC Santa Barbara, to ask what could have happened. “It most likely sank,” she told me. Scientists aren’t sure exactly why, but every once in a while, mucilage mats will just drop back below the water’s surface.
To follow the fate of the mucilage, I reached out to Serço Ekşiyan, who has been diving in the Sea of Marmara for half a century. We sat in his wooden boat, which he had bought used and restored, as it bobbed in its slip at a derelict fishing harbor. His dives have always had a purpose: As a teenager, he went spearfishing to sell fish to restaurants; later, he spent years clearing abandoned nets from the sea and transplanting threatened coral to a marine reserve that he helped establish.
I asked him if the mucilage had really sunk. “It’s true,” he said. When floating at or just below the surface, the mucilage can be up to 30 meters thick, but as it sinks, it compresses into a denser, thinner layer less than 10 meters thick. Ekşiyan’s dives are now spent documenting the mucilage with a homemade GoPro fashioned from a security camera and a plastic case. He showed me a compressor he uses to fill the oxygen mask that he made from Cold War–era U.S. Air Force plane components that had been sold to the Turkish military.
Diving in the mucilage, Ekşiyan said, is like drifting through a nightmare; the mucilage hangs in massive webs, and even at noon the visibility is so low that it can feel like diving at night. As the mucilage continues compressing and sinking, it blankets the seabed. There, it blocks the entrances to caves and caverns, evicting fish from their homes. As the mucilage continues to decompose, it consumes oxygen, creating a dead zone—an area without enough oxygen to sustain life. The coral Ekşiyan had transplanted bleached due to the mucilage and abandoned nets, but it managed to survive—for this year. “And the reefs,” he said, “are like abandoned villages.”
Asutay Akbayır, the regional manager of the Professional Association of Diving Instructors diver-training organization, comes from a family of divers; like Ekşiyan, he has been diving in the Marmara for decades. Even before the mucilage outbreak, he told me, diving instructors and guides were losing their jobs because of the pollution in the Marmara. “Most of the divers, they don’t prefer to dive in challenging environments where the visibility is very low,” he said. “You are not even able to see your own hand when you dive, your own body.” But Akbayır hopes that recreational diving will evolve, not disappear. Maybe, he said, divers will become ambassadors for the sea, telling the public about the devastation taking place underwater.
What I’d been looking at all summer, I realized, was not only an unfamiliar phenomenon but also an unfamiliar kind of death. To confront global warming is to confront death, and it will show up in surprising places and forms—some painful, some disgusting, some disorienting. We talk about preparing for climate change, but how can we prepare for endings we can’t yet imagine?
By summer’s end, life above the surface felt normal. The sea was clear and the beach clubs were packed. People ordered fish at restaurants with abandon. It was as if the sea-snot outbreak had never happened. In May, it had been an international story; by July, only the Turkish media were paying close attention; and by September, it had ceased to be a regular topic of conversation.
In many bodies of water around the world, it was a summer of extremes. Red tides appeared in Florida; algal and bacterial blooms in dozens of reservoirs, lakes, and ponds in Massachusetts; and toxic blue-green algae in Lake Superior. As of October, 476 toxic-algae outbreaks had been reported in the United States, the second-highest number on record. Glacier scientists are investigating the appearance of pink ice at Italy’s Presena Glacier, an Alpine region known for skiing and outdoor sports. Research suggests that the algae could contribute to increased glacial melt.
A recent study published by a team at the Swedish Museum of Natural History, in Stockholm, and the University of Nebraska at Lincoln argued that these extreme blooms, and the dead zones left in their wake, parallel the beginnings of the worst extinction event in Earth’s history—the Permian-Triassic extinction, which happened some 252 million years ago and is sometimes called the “Great Dying.”
In September, just as the Turkish summer was shifting into fall, I got a phone call from Mustafa Yucel, the marine-science professor, who was inviting me to meet him and his team when their research vessel docked at Istanbul’s Port of Haydarpaşa. They had spent a week at sea checking their observation stations, and they reported that most of the mucilage was gone—likely consumed by bacteria and fish.
“But the conditions that led to this mucilage bloom are still present,” Yucel cautioned. The more pressure put on a marine system, the more prone it is to an extreme reaction: a mass die-off of sea life or an outbreak of chunky, stinking mucilage. Or both. “The Marmara is now an extreme ecosystem—extreme in algae, bacteria, and lack of oxygen. That’s why it’s hard for us to predict what’s next,” Yucel said. “The sea snot may come back, because the conditions are there, but it could just as easily be some other extreme—hydrogen sulfide, a red tide, massive fish kills rotting on a beach … Disgusting events will increase in frequency and magnitude.” And as they do, they will also become more and more unmanageable.
“Whether we directly attribute it to climate change or to pollution, mucilage is a symptom of the unsustainable use of our planet,” says Antonio Pusceddu, a marine biologist at Italy’s University of Cagliari and one of the world’s handful of mucilage experts. “The rate at which our planet changes now is unprecedented.” Though Turkey’s mucilage outbreak is the worst on record, smaller outbreaks have occurred along the coast of Australia and in the Mediterranean. When one particularly large and disruptive outbreak hit Italy’s Adriatic and Tyrrhenian coastlines in 2009, Pusceddu and his colleagues investigated the relationship between climate change and the frequency of mucilage outbreaks in the Mediterranean Sea over the past two centuries. They found that the number of outbreaks had increased almost exponentially in the previous 20 years. But over the past decade, he told me, better wastewater treatment has reduced or eliminated the occurrence and severity of mucilage in Italy.
In response to the sea-snot saga, the Turkish government designated the Marmara Sea as a special environmental-protection zone. That status requires a tighter review process for commercial maritime activity, more factory inspections and fines, and an increase in the percentage of water flowing into the Marmara that receives advanced biological treatment from 46 to 100 percent within three years. But how these measures will be funded or enforced remains unclear.
After talking with Yucel and his colleagues in the Port of Haydarpaşa, I stepped off their research vessel and looked back at the Marmara. I wanted to feel the same relief as the rest of Istanbul, to jump back into the sea and float in its tides, staring up at the blue sky. I wanted to believe that the water was clean, that the source of the disgusting ooze was gone. But instead, as I looked at the water, I felt something rise up inside me, a new feeling of disgust. Only this time, it wasn’t a reaction to the mucilage. As long as humans continue polluting and heating the sea, marine ecosystems will become more delicate and less predictable. Each outbreak shows us the consequences of our own actions—if we choose to see them.
This Atlantic Planet story was supported by the HHMI Department of Science Education.