Lurking in the sewer systems under your feet could be a threat so horrifying, so disgusting, that the mere mention of it sends a shiver down the spines of sanitation specialists everywhere: Fatbergs, mounds of grease capable of growing to massive proportions and blocking the flow of sewage with expensive—and potentially disastrous—consequences. Here’s what you need to know about fatbergs, and how you can help prevent them.
1. The word fatberg was coined in 2008.
It takes inspiration from the word iceberg, and first appeared in print in a story referencing photos of pollution on a beach in the January 22, 2008 edition of the Birmingham Post: “particularly memorable are the large, rock-like lumps of cooking fat [Alistair] Grant calls ‘fatbergs,’” the paper said. The word was added to the Oxford English Dictionary in 2015.
2. Fatbergs are made of fats, oils, and greases, or FOG.
“Fatbergs form from a buildup of fats, oils, and greases—called FOG for short—in the sewer pipes,” says Kimberly Worsham, founder of FLUSH (Facilitated Learning for Universal Sanitation and Hygiene), a company that, through edutainment events and advisory consulting, aims to change how the world perceives and does sanitation work. “This can include soap scum, dairy dregs, congealed fat from food, industrial grease, etc.”
Lots of the grease comes from restaurants whose sinks aren’t equipped with grease traps, but individual households contribute to fatbergs, too. “Your Thanksgiving food scraps are part of the next fatberg,” Worsham tells Mental Floss by email. “There’s a lot of fat in our holiday meals that are prime for fatberg parties in the sewers—all because we’re lazy and don’t want to open the trash bin.”
All that FOG, along with human waste, settles into crevices in the sewer pipes. The fat interacts with calcium—which can either come from concrete pipes or water in the system that has flowed over concrete—and undergoes the process of saponification, or turning into soap. “After a while, more FOG bits build up together on the sides of the pipes, creating congestion in the sewers,” Worsham says.
3. Fatbergs are as old as sewers.
“Fatbergs have been around since as long as humans had sewers—at least since the Roman Empire had its Cloaca Maxima,” Worsham says. “We have evidence that Roman slaves would have to go pull out the stuck fatty bits from the sewers. Fatbergs were actually the reason a guy developed the grease trap in the 1880s because he was rightfully sure that fat would destroy the sewer systems eventually. But most fatbergs were relatively small compared to the ones we see nowadays—the magnitude has just increased a ton in the last decade or two.”
4. We have wet wipes to blame for today’s fatbergs.
Wet wipes are a scourge upon the world’s sewer systems. Despite what their packaging claims, wet wipes are not flushable—and doing so has contributed to fatbergs in a big way. “We started seeing the instances of these larger and sometimes mega fatbergs popping up in big cities like London around the time the popularity of adults using wet wipes really started to boom, which was about a decade ago,” Worsham says. She describes wet wipes as “absorbent cotton bastards” that, unlike toilet paper, don’t dissolve in water but instead are great at grabbing grease. “Imagine a bunch of fat-soaked wet wipes in a sewer about 2 feet wide—they’re going to get together and clump up.” Because they don’t dissolve, wet wipes also wreak havoc on our waste treatment plants.
5. Weird things are found in fatbergs.
People put a lot of things in their toilets, so a wide range of stuff has turned up in fatbergs, including condoms, tampons, dental floss, syringes, drugs, and wet wipes. Bones and false teeth have also been found in fatbergs, as have a typewriter and a bowling ball. “I think the fact that they’ve found stuff like whole toilets and mop heads in fatbergs is pretty weird—it’s very meta,” Worsham says. “Those probably somehow fell through a manhole or something, maybe.”
The composition of fatbergs, along with their size and even color, vary largely, and depends on the community where it formed. “We’re still learning quite a lot about fatbergs, and really fatbergs are not homogenous in their contents at all!” Worsham says.
But there are still some insights we can glean from them—like whether there are a lot of restaurants in an area, for example. “Some things they do find in some of the fatbergs are concentrations of drugs in certain regions,” Worsham says. “There’s this story about the South Bank fatberg in London that had a lot of performance enhancement drugs in it—more than other drugs like cocaine and MDMA—and I recall people speculating was because that was connected to an area of London that has a lot of clubs and public places where the area has a fit culture.”
6. Fatbergs can take a while to form.
According to Worsham, how long a fatberg takes to form depends on things like the type and size of pipes and what, exactly, is going into those pipes. “In London, some of the bigger fatbergs that they’ve pulled out—those 130 tons or more—took probably about a decade to create,” she says. “But I’m sure in a lot of places it takes much less time, especially in places where the pipes are smaller, and people are more careless with dumping stuff into sewers.”
7. Fatbergs show up in sewer systems around the world.
In the United States, fatbergs have been found in Baltimore, Maryland; Charleston, South Carolina; New York City; and Fort Wayne, Indiana. Around the world, these massive mounds of fat and trash have plagued sewage systems in Canada, the UK, Singapore, and Australia. (A fatberg the size of a gas tanker truck, found in Melbourne in April 2020, is thought to have grown so big due to a toilet paper shortage brought on by COVID-19, which spurred people to buy more wet wipes.)
8. Fatbergs smell awful.
Worsham has never encountered a fatberg herself (“that could be either a good thing or a bad thing knowing me, I guess,” she says), but those who have likely wish they could forget the stench. John Love, a professor at the University of Exeter who was part of a group of scientists that performed a study on portions of a fatberg found in the sewage system in Sidmouth, England, told The New York Times that “It was my first time analyzing a fatberg, and when you smell it, you think this is going to be the last time because the smell was honking. It was awful to do, it smelled gross.” The Guardian described the smell as “a heady combination of rotting meat mixed with the odor of an unclean toilet,” while the BBC said it’s “a bit like vomit, with undertones of poo.”
9. Finding a fatberg can be a shock.
What’s it like to come upon a fatberg in a sewer? Charlie Ewart, a sewer worker in southwest England, found a 209-foot-long fatberg in Sidmouth when he went through a manhole in January 2019. He described his experience to The Guardian:
“I saw it and thought: ‘What on Earth?’ It was completely unexpected … It’s really eerie in that bit of the sewer and it does look like something out of a horror scene, all congealed and glossy and matted together with all kinds of things.”
10. Fatbergs can be massive.
It can be hard to comprehend just how big these masses of fat and debris can grow, so some comparisons can help helpful. According to Newsweek, fatbergs can reach 800 feet long, stand 6 feet tall, and weigh as much as four humpback whales. Other fatbergs in the UK have been as big as airplanes and double-decker buses and longer than the Leaning Tower of Pisa is tall. One fatberg found in the sewers under Liverpool weighed as much as 13 elephants.
11. It’s not easy—or cheap—to remove a fatberg.
Removing these giant masses clogging the sewers is no easy task. “My understanding is that they have to be removed really slowly, and with blunt force,” Worsham says. “You don’t want to break the sewer pipes by chiseling away with sharp stuff—that kind of defeats the purpose.”
Workers must don special suits to protect themselves against the contents of the fatbergs—which could potentially include things like needles—as well as noxious gases and fumes. Then, crews of workers use shovels and other blunt objects to chip away at the mass. “They’re often hard, so it takes a while,” Worsham says. “Think weeks, or maybe even months if it’s big enough.” The process is time-consuming and expensive: Cities spend millions of dollars a year fighting fatbergs. “Scientists are trying to figure out how to create bacteria that can eat up the fatbergs without needing to put people into the sewer to manually remove it,” Worsham says.
Once a fatberg is removed, “Places either study them to understand them, or they go into landfill[s],” Worsham says. “There are stories that in China, they scoop up the fatberg oils from sewers and crudely refine them to use at sidewalk food stalls as gutter oil … so there’s that.”
In 2018, scientists at the University of British Columbia developed a method for turning fatbergs into biofuel and implemented it in pilot testing programs, but there’s more work to be done in that area.
12. Fatbergs are dangerous.
As fascinating as fatbergs are, there’s no question that they’re bad news. “Fatbergs work like the clogging of a heart artery,” Worsham says. “If we don’t move them, they start to build up, and the sewer system has something like the equivalent of a heart attack.” With no way to get through the fatberg, the waste in the sewer backs up into your home and the surrounding environment, including waterways and wetlands.
“There’s still pathogenic poo in the fatbergs, too, on top of other wacky and hazardous things like needles,” Worsham says. “Once the fatbergs cause sewage spills, those pathogens become intermingled in our communities and surroundings, and we can get sick from that.”
Then there’s the fact that fatbergs are dangerous to the people removing them: “If you’re a sewer worker trying to clean up a fatberg, getting pricked by a sharp object in a fatberg has more personal and acute dangerousness to it—you don’t know what is in the needle, or who was using it, or why they were using it, or how,” she says.
13. A fatberg was put on display in London.
In 2017, workers discovered an 820-foot fatberg in the sewer system under London’s Whitechapel neighborhood, which took nine weeks to clear. A piece of that fatberg, which was nicknamed “The Beast” and “The Monster of Whitechapel,” went on display at the Museum of London in 2018. The exhibit was aptly called “Fatberg!” and featured a mannequin dressed in protective gear alongside the tools needed to get rid of a fatberg. The specimen itself was contained in a special sealed unit that was placed inside a display case.
“Displaying part of a fatberg has been on the museum’s wish list for a few years and when we heard about the Whitechapel fatberg—the biggest one ever found in the UK—we knew we had to act quickly to secure a sample,” curator Vyki Sparkes said in an interview on the museum’s website. “It’s grand, magnificent, fascinating, and disgusting. The perfect museum object!”
Flies hatched from the fatberg while it was on display; the specimen also changed color and sweated a bit. According to collections care manager Andy Holbrook, who is the only person to handle the fatberg outside of the display, and had to wear full protective gear while doing so, “The fatberg samples were lighter than they looked, it felt a little bit like pumice stone, but crumbly in texture. But Fatberg has evolved since it’s been on display.” When it was first acquired “it was waxy and wet,” but a year after its removal from the sewer, it was “much lighter, with a bone-like color and the texture has become like soap.”
These days, the fatberg is off display and in quarantine under Holbrook’s supervision. It’s the only item in the collection with a livecam (called the “Fatcam”), which you can watch here. The fatberg was air-dried to preserve it, but that hasn’t stopped it from changing—in fact, it’s developed a toxic aspergillus mold “in the form of visible yellow pustules,” according to the museum’s website.
14. Scientists are studying fatbergs.
There’s a ton we don’t know about fatbergs. “We don’t understand how to get rid of them cheaply, what happens to them over time and how they evolve, or all of the things they could potentially tell us about our communities,” Worsham says.
But science is on the case: In addition to performing “autopsies” on fatbergs, scientists have also performed molecular analysis on a fatberg, which revealed the presence of parasite eggs and bacteria like Campylobacter, E. coli, and Listeria, as well as antibiotic-resistant bacteria. Scientists have even analyzed the DNA of a fatberg. Worsham likens it to “a new kind of forensics study.”
15. You can help stop fatbergs.
Are you concerned about having sewage backing up into your home or business after reading this piece? There’s action you can take.
The No.1 thing commercial businesses can do to stop fatbergs is to install grease traps. “A lot of fatbergs in recent history have been located near restaurant districts, and restaurants dump their fats and oils down the drain. So, don’t do that, and that helps prevent fatbergs a lot,” Worsham says.
Individuals can do their part, too, by not throwing just anything in the toilet. “Our sewers are often used as trash bins, but they don’t work the same way. That means you need to not flush anything down the toilet that’s not coming directly out of your body, water, or isn’t legitimate toilet paper. Literally, nothing else can go down the toilet,” Worsham says. “And when you’re putting stuff down the drain, don’t dump coffee grounds, tea leaves, whole bits of foods and fats, or any of that stuff. You’d be surprised how things easily bind up fats and greases in the sewers. For instance, floss works almost like a lasso, binding up fats together that can contribute to larger fat stores.”
Finally, Worsham says, “please, never ever put wet wipes down the toilet. Personally, I’m a big bidet fan and I think that everyone should dump their wet wipes habit and start using bidets. They’re glorious.” If you’re interested in buying a bidet, we have a few recommendations here.