What is a Fatberg? Meaning, Waste and What It’s Made Of

Over the last 20 years or so, changes in our eating habits and the products we use in our households have combined to create an out-of-sight phenomenon in our sewers: fatbergs. But what is a fatberg, how do they form and what is a fatberg made of?

In this blog post, the grease management experts here at Aqua Mundus are going to break down exactly what a fatberg is, why they can cause so much trouble and the best ways to prevent fatbergs in the first place. We’ll cover fatberg meaning and legal compliance, so let’s get started. To learn how to get rid of fatbergs, check out our blog post.

‘Fatberg’ is the colloquial name given to a major obstruction in a municipal sewer system caused by the amalgamation of flushed items and the abundance of food waste products.

The term ‘fatberg’ is now a common colloquial term used in the UK water industry, but where did it come from? The word is actually a combination of ‘iceberg’ and ‘fat’, creating ‘fatberg’, meaning a very large amalgamation of fat and other waste. 

Fatbergs are essentially created from a meeting of sewer contraband; items that really shouldn’t be in the sewer to begin with. These items can snag, congeal, become trapped and assimilate, leading to the growth of a major blockage, all exacerbated by Britain’s ageing sewer network.

Common components include food sediment, fats, oils and grease that have made their way into the sewer from household and even commercial kitchen wastewater lines, and flushed items like wet wipes, cotton buds and even nappies that should never have been flushed to begin with.

Fatbergs can be made of a wide variety of materials, including anything that can become lodged and begin to gather fats and grease: 

In short, anything that can’t naturally break down or degrade is potential fatberg waste. These items can get caught, bind together and act as a trap for FOG, which leads to the accumulation of a fatberg. 

Each fatberg will look slightly different depending on the materials it’s formed from, but there will be large similarities. Generally, fatbergs appear as solid, rock-like masses with a grey or whitish colour. Much like actual icebergs, they sit above and below the waterline and can grow to massive sizes. 

As well as causing physical blockages to sewer networks, fatbergs also emit a strong, foul smell. 

At their core, fatbergs are caused by materials that don’t belong in the sewer system combining to form major blockages.

One of the biggest issues stems from the way water acts. Even in the smoothest pipes, water flows slightly slower when in contact with the pipe than in the middle of the channel. This isn’t really an issue in smooth, modern pipes as the difference is negligible, but in older sewers with ageing brickwork, cracks and other impediments to flow, it can slow considerably at the edges, leading to turbulence that can trap solids.

As wastewater continues to flow over trapped solids, other impurities and non-biodegradable solids begin to amalgamate, growing the obstruction in size and causing even more items to be captured. Once a formation is at this stage, it becomes inevitable that it will continue to grow until it is eventually detected and removed, usually at great cost to the water company and major inconvenience to those who rely on the sewer.

Until something goes wrong, it’s hard to detect a fatberg, meaning they’re usually only spotted when a sewer has almost completely been blocked, flooding the local area and causing significant issues for human and environmental health.

Fats, oils and grease (FOG) enter sewers through improper disposal in commercial kitchens and households. Once in the pipes, they cool and solidify, sticking to surfaces and creating a sticky base that attracts other debris.

Wet wipes, sanitary products, cotton buds and even dental floss and razor blades can contribute. Despite being labelled ‘flushable,’ many do not break down in water and will combine with FOG to create larger, harder masses.

The UK presents prime fatberg creation conditions. Increases in household FOG production in recent decades combined with an ageing sewer system mean that fatbergs are becoming increasingly common. There has also been a marked increase in the usage of non-biodegradable wipes and other products, which shouldn’t be flushed down drains. 

In 2025, Thames Water found a 100-tonne fatberg lingering beneath the streets of London, in one of the worst recorded fatberg incidents that took over a month to clear. 

We create a lot more FOG as a nation than we used to, so businesses that cook hot food should capture FOG before it gets into the sewer. This is why commercial kitchens are legally required to have grease traps or interceptors installed. These devices, which have been around for over 140 years, will capture and hold FOG and food sediment while decontaminated water continues flowing.

Now we’ve covered ‘what is a fatberg?’, let’s look at how to prevent them. One of the simplest ways, apart from not flushing inappropriate waste, is grease traps.

Grease traps are a straightforward piece of drainage technology. They prevent FOG from reaching the sewer network by catching it in a specially designed tank. This way, it can be gathered and properly disposed of before it ever enters the public sewer system. 

Not only does this help prevent blockages, it helps ensure businesses stay compliant with strict legislation. For more guidance on fatberg prevention and legislation, head over to our blog post. 

Fatbergs, and the issues they cause, are preventable with the right installation in your commercial kitchen. Here at Aqua Mundus, we have over 25 years of experience in the waste management industry, and there’s nothing we don’t know about buying, installing and managing a grease trap.

If you have any questions, need to talk to an expert about your state of compliance or would like to book a free on-site survey for your waste management setup, get in touch with Aqua Mundus today.