How The Thames Went From Being Biologically Dead To One Of The World’s Cleanest Rivers In 60 Years

Between 1961 and 1995, regulations helped to increase water quality standards by treating all sewage entering the Thames. This is the story of how the Thames went from being ‘biologically dead’ to one of the world’s cleanest rivers in 60 years.

How The Thames Went From Being ‘Biologically Dead’ To One Of The World’s Cleanest Rivers In 60 Years

It may amaze you to learn that the River Thames is regarded as one of the cleanest rivers in the world. What is more astonishing is that it achieved that position just 60 years after researchers at London’s Natural History Museum proclaimed it “biologically dead.” Despite this extraordinary comeback, there is no space for complacency: pollution, plastic, and a growing population continue to pose new and growing risks to the Thames.

From Kemble in Gloucestershire to Southend-on-Sea in Essex, where it runs into the North Sea, the Thames extends for almost 360 kilometers. Since medieval times, it has been under pressure from increasing numbers of city people as it bisects London.

The river became a waste dump, with leaky cesspits and discarded trash turning several of its branches into sewers. The Fleet, which runs from Hampstead to Blackfriars and into the Thames at Blackfriars, is arguably the best recognized of these minor rivers, which today lie beneath the streets of London, long covered up to disguise their filthy odors.

The final nail in the coffin was the scorching summer of 1858, known as the Great Stink, when the river’s excessive levels of human and industrial trash pushed residents out of London. Sir Joseph Bazelgette, a civil engineer, was tasked with constructing a sewage system to remedy the situation, that is still in operation today. Over a century of network enhancements followed, including improving sewage treatment plants and connecting household toilets to the system.

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During WWII, bombings across the city ruined parts of the network, enabling raw sewage to flow back into the river. Furthermore, as the Thames expands and slows as it passes through downtown London, fine sediment particles from its tributaries accumulate on the riverbank. These were and continue to be extensively contaminated with heavy metals (read below) from highways and industries, resulting in a poisonous aquatic environment.

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World War II Blitz in East London. Photo credit: Wikimedia Commons

The water in which most fish reside should contain a minimum 4 milligrams-5 milligrams of dissolved oxygen per litre for them to survive. During the 1950s, measurements revealed that dissolved oxygen levels in the Thames were just 5% saturated, or 0.5 mg/l. As a result, only a few aquatic invertebrate species, such as midges and fly larvae, could survive in the river.

Dissolved oxygen levels weren’t really detectable throughout the 20-mile stretch of the Thames that runs through central London. In the 1950s, no fish were documented from Kew to Gravesend, a 69-kilometer stretch of river. The River Thames was declared “biologically dead” after surveys in 1957 revealed that it was unable to support life.

Turning tides

The river’s fortunes began to alter after a lot of work from policymakers. Between 1961 and 1995, regulations helped to increase water quality standards by treating all sewage entering the Thames.

Under British Prime Minister Margaret Thatcher’s privatization of water businesses, the National Rivers Authority was established in 1989, as well as biotic monitoring. This is a sophisticated scoring system that analyzes pollution by counting the macroinvertebrates found in a river, such as mayflies, snails, and water beetles, and assigning a score to each species based on their tolerance for low dissolved oxygen levels. Low total scores indicate that the river is less healthy since it is unable to support creatures that require oxygen.

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Running through central London, the Thames carries a number of invertebrates – including plenty of leeches. Photo credit: Veronica Edmonds-Brown/ Author provided

As a result, the construction of massive oxygenators, or “bubblers,” to raise dissolved oxygen levels was one of the defining moments in the Thames’ health. In the early 1980s, the Thames Water Authority created a prototype oxygenator based on a river barge. In 1988, it was replaced by a self-propelled “Thames Bubbler,” and in 1999, a third vessel was launched. They are in charge of ensuring that there is enough oxygen in the water to support expanding fish populations.

The flounder was the first fish species to return to the Thames estuary and lower Thames in 1967, followed by 19 freshwater fish and 92 marine species such as bass and eel. The reintroduction of salmon in the 1980s was a wonderful milestone for environmentalists, and today, about 125 species of fish are frequently reported, with exotic species such as seahorses being spotted on rare occasions.

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Bream, pike, salmon, perch, dace, eel and trout are among the species that can now be found in the Thames. Photo credit: Peter O’Connor/Flickr (CC BY-ND)

On the surface, this is a tremendous turnaround. However, there are still unaddressed issues with toxic sediments entering the river. Despite the fact that many industries that had been pouring garbage into the Thames closed during the 1990s recession, water pollution levels have not greatly decreased since then. Heavy metals, for example, can cling to clay particles in riverbeds for decades, damaging or killing species that consume them.

Because most invertebrates cannot survive or reproduce in such a poisonous environment, the river’s biodiversity is dominated by leeches and fly larvae. Microplastics and water-soluble drugs like Metformin, which sewage treatment plants are unable to filter out, are two more harmful contaminants. These drugs have not been studied to see how they affect aquatic life.

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Seals have been spotted swimming along the length of the Thames. Photo credit: Tambako the Jaguar/ Flickr (CC BY-SA)

A system built for less than five million people but now used among over 10 million people has overstretched both sewage and surface water drains across Greater London. To manage the additional load, a new 25-kilometer “super sewer” is currently being built beneath London. Despite the fact that it is projected to be completed by 2025, it will not suffice on its own.

If we want to protect London’s iconic river’s hard-won health, we ought to invest more in new drainage infrastructure across the city to minimize damage from increasingly common storm surges and overflows.

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  1. This is a different problem than that faced by the Indian government. Construction of mass crematories at Varanasi could put the Ganges on course to purify itself in one lifetime. These could be run by the priesthood, with income-based fees, and stiff fines for those dumping cadavers into the river. India will clean up when traditionalists understand that “custom” is no excuse for pollution.

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