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LONDON — Its smell is even more impressive than its size.

Stretching longer than the length of two football fields, a 130-ton mass of congealed oil, wet wipes, diapers and sanitary products colloquially known as a "fatberg" risks blocking up a Victorian-era sewer under the streets of London.

Workers dressed in layer after layer of protection and oxygen masks are shielded from the worst of the stench. But a piece of "fatberg" brought up to the surface infected the area — and prompted gagging and retching more than 50 feet way.

As hard as concrete, the "fatberg" is so compacted that workers used a saw to cut small pieces off the mass Wednesday afternoon. High-powered jet hoses break it up while an industrial vacuum sucks chunks to ground level.

The U.K. capital's system of tunnels and sewers goes largely unnoticed by the city's 8.7 million residents — at least until something goes wrong.

This "fatberg" was discovered earlier this month about 19 feet underground in the Whitechapel area of east London.

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“This sewer is about a meter high and the 'fatberg' comes about two-thirds of the way up,” said Alex Saunders, a sewer network manager for utility Thames Water. (A meter is a little longer than a yard.)

It took about a year for the jam to accumulate.

“By catching it this early we were able to start dealing with it before it fully blocks the sewer," Saunders added. "When we’re too late ... that’s when you get sewage backing up into properties and flooding in the environment."

Part of the "fatberg" that was removed Wednesday. Rachel Elbaum / NBC News

Each shift, workers climb down a small brick shaft into the sewer and remove several tons of the blockage.

Authorities predict it will take three weeks to clear it entirely.

“The fat smells worse than the fecal matter,” said David Mimms, an on-site team manager for Thames Water.

For centuries, Whitechapel has been home to successive waves of immigrants, with each group making their mark on the city, both above and below the streets.

Now home to a large Bangladeshi community, restaurants line the streets, along with shops selling traditional South Asian clothing and shoes.

But officials say too many food establishments dispose of their cooking oil down the drain.

According to Thames Water, if you live within 50 yards of a food establishment then you are eight times more likely to be flooded by sewage.

The "fatberg" is made up of congealed fat, baby wipes and other materials people flush down the toilet or put down the drain. Thames Water

Though they will ultimately benefit from the operation, locals weren’t exactly thrilled with the work — which is being carried out near a small street market selling head coverings, long robes and gold jewelry.

“It is smelly and it keeps customers away,” said Mohammed Ali, who runs one of the stalls. “This week is at least less smelly than last.”

The stench doesn't worry the Museum of London, which wants a piece of the "fatberg."

“We are interested in the challenges facing the modern city, what happens when a city changes rapidly,” said Alex Warner, the museum's curator. “This is exactly the type of thing that we use to get the public talking about the materials that we dispose of. It will be an impact object on display.”