Thames Pollution: A Troubling Reality Check

The River Thames, which runs through London, has had a long history of pollution. In 1858, the river was clogged with sewage, causing an infamous Great Stink that drove people out of the city. While the river has seen improvements since then, with the installation of large oxygenators and efforts to reduce industrial discharges, it continues to face challenges. Today, the Thames is impacted by storm-sewage pollution, where rainwater and wastewater overflow into the river when the sewage system reaches capacity. This has led to concerns about high levels of bacteria and viruses, such as norovirus and E. coli, as well as the presence of microplastics and heavy metals. Despite these issues, the Thames has been described as one of the world's cleanest city rivers, supporting a diverse range of wildlife, including seals and migratory birds. However, the increasing population and new threats from pollution and climate change continue to pose risks to the river's health.

The Thames Tideway Tunnel aims to address the issue of storm-sewage pollution

The River Thames has a long history of pollution. In the past, domestic and factory waste would flow through the streets and seep into the groundwater, with the Thames's tributaries becoming dumping grounds. In 1878, the passenger steamer Princess Alice sank in the Thames at a point where sewers released waste into the river. Many survivors of the initial collision died after ingesting the polluted water.

By the 1960s, the Thames was once again notably polluted, with the Port of London Authority and London County Council taking steps to improve sewage treatment and industrial pollution. However, the problem of sewage pollution in the Thames persists to this day. London has a combined sewage system, meaning that rainwater and wastewater flow together in the same pipes. This system was built for Victorian London when the population was much smaller. Today, the sewage system is stretched to capacity by the amount of sewage produced by London's modern population. When it rains, the pipes, which are already full, do not have the capacity to hold the rainwater as well. To avoid rainwater and sewage from flooding homes, the mixture is discharged into the Thames, known as storm-sewage pollution.

The Thames Tideway Tunnel, also known as the "super sewer", aims to address this issue of storm-sewage pollution. The tunnel is nearly 16 miles (26km) long and stretches beneath the River Thames, connecting 34 storm overflow drains. It intercepts outflows from London's most polluting combined sewer overflows (CSOs), stores them, and directs them to sewage treatment works for processing. By capturing and treating the sewage before it enters the river, the tunnel will help to clean up the Thames and improve its health. The tunnel has a combined capacity of 1.6 million cubic metres, protecting the Thames from sewage pollution.

The Thames Tideway Tunnel is part of a larger project called the London Tideway Improvements, which also includes the Lee Tunnel, a 6.9km (4.3mi) tunnel with a capacity of 16 million tonnes annually from the greatest-polluting CSO point in London. The London Tideway Improvements plan was created in the early 2000s, with five Thames Water sites upgraded in 2014, and the Lee Tunnel built in 2016. The Thames Tideway Tunnel was completed in March 2024, with testing beginning in the summer of that year. It became fully operational in 2025.

The river contains high levels of norovirus, E. coli, and other harmful bacteria

The River Thames has long been a hub for trade, a source of water and food, and a place for pageantry. However, it has also been London's sewer for hundreds of years. Despite improvements in sewage treatment and industrial pollution, the Thames continues to face significant pollution challenges.

One of the major issues is the presence of harmful bacteria in the river, including norovirus and E. coli. TV naturalist Steve Backshall, who lives next to the river with his wife, Olympic rower Helen Glover, has described the Thames as "toxic". Samples he took from the river were analysed by Bangor University's wastewater research centre and revealed high levels of potentially harmful bacteria. The test results were described as "a death potion" for the river, with the potential to lead to the "total annihilation of the ecosystem".

In particular, the study found an extraordinarily high estimated 39,000 gene count per litre of norovirus in the river, far exceeding the 10 gene count per litre required to make a human ill. This poses a significant health risk to anyone coming into contact with the water, including wild swimmers and rowers.

Water quality testing by River Action has also found alarmingly high levels of dangerous E. coli bacteria from sewage pollution. The tests revealed levels of E. coli up to 10 times higher than what is considered acceptable for designated bathing waters. The high levels of E. coli have spread fear among competitors in the historic Gemini Boat Race between Oxford and Cambridge universities, with some calling for improved water quality across the country.

The presence of harmful bacteria in the Thames highlights the urgent need for action to protect the health of those who rely on the river for work, recreation, and water supply. While efforts are being made to address pollution, such as the work of organisations like Thames21, more needs to be done to ensure the Thames is safe for all who depend on it.

Thermal pollution unnaturally warms the water, which can negatively impact river life

The River Thames has a long history as London's sewer, with a significant presence of bacteria and other pollutants. In the past, the Thames would have been affected by pollution from industry, which would have killed all wildlife. Today, the water is expected to be neutral (neither acid nor alkali), which is better for wildlife.

However, the river continues to face pollution issues, with sewage still entering the Thames when the system reaches capacity at overflow points along the river. This is known as stormwater sewage pollution. The capital's sewage system is stretched to capacity by carrying the sewage produced by London's modern-day population.

Thermal pollution is a significant concern, as it unnaturally warms the water and can negatively impact river life. Thermal pollution occurs when the temperature of a natural water body changes significantly, which can severely impact aquatic life and water quality. The primary causes of thermal pollution are natural events and human activities, such as discharging warm wastewater and using water for industrial cooling. Power plants and factories, for instance, use water for cooling, and this heated water is then discharged back into the river, raising the overall temperature and impacting aquatic life.

In the case of the Thames, a possible source of thermal pollution is rainwater runoff, which is heated up as it moves across warmer roads and ends up in the river. This heated rainwater raises the river's temperature, reducing the amount of dissolved oxygen available for fish and other aquatic life. The Thames Tideway Tunnel is being constructed to address the issue of sewage pollution in the Thames, with the aim of redirecting sewage from overflow points to pre-existing treatment plants.

The Thames has been described as biologically dead due to high levels of pollution

The River Thames has been described as biologically dead due to high levels of pollution. In 1858, the river was clogged with sewage, causing the "Great Stink" that drove people out of London. This prompted the construction of a sewage network, which is still in use today. However, the system has not kept up with London's growing population, leading to continued sewage overflow into the Thames.

In addition to sewage, the Thames has also been contaminated by industrial waste and runoff from roads. This has resulted in high levels of pollution, including heavy metals, microplastics, and water-soluble medicines that are toxic to aquatic life. While efforts have been made to improve water quality, such as the installation of oxygenators, the river still faces threats from pollution and climate change.

Bangor University's analysis of water samples taken near the border between Berkshire and Buckinghamshire revealed high levels of norovirus and E. coli. The study also found an extraordinarily high estimated 39,000 gene count per litre of norovirus, far exceeding the amount required to make a human ill. These findings highlight the serious health risks associated with the pollution in the Thames.

Despite these challenges, the Thames has been making a gradual recovery. Oxygen levels necessary for fish are increasing, and dangerous phosphorus levels are decreasing. The river is now home to a diverse array of wildlife, including seals and migratory birds. The expansion of sewage treatment plants and limits on industrial discharges have contributed to these improvements.

However, there are still concerns about the long-term impact of pollution on fish populations and the potential effects of climate change on the estuary's wildlife. The Thames Tideway Tunnel, also known as the "super sewer", is currently under construction and is expected to capture and store the millions of tonnes of raw sewage that overflow into the estuary. This project offers hope for further improving the water quality of the Thames and mitigating the effects of pollution.

The river contains high levels of microplastics, which can harm aquatic life and birds

The River Thames has a long history of pollution. In the past, the Thames would have been affected by pollution from industry, killing all wildlife. In the 1800s, as London's population grew to over 2.5 million, the river became a dumping ground for domestic and factory waste. This problem persists today, with sewage still entering the river when the system reaches capacity.

The Thames contains high levels of microplastics, which can harm aquatic life and birds. Microplastics have been shown to have negative effects on the health of aquatic organisms, including fish and invertebrates. In aquatic invertebrates, microplastics cause a decline in feeding behaviour and fertility, slow down larval growth and development, increase oxygen consumption, and stimulate the production of reactive oxygen species. In fish, microplastics can cause structural damage to the intestine, liver, gills, and brain, affecting metabolic balance, behaviour, and fertility. The degree of harm depends on the particle sizes and doses, as well as the exposure parameters.

The prevalence of microplastics in fish may also have implications for human health, as fish is a major source of protein for humans. Microplastics have been shown to cause tissue damage, oxidative stress, and changes in immune-related gene expression in fish.

The high levels of microplastics in the Thames are a serious cause for concern, threatening the health and survival of aquatic life and potentially impacting human health. The sources of these microplastics should be addressed to reduce their presence in the river and mitigate their harmful effects.

Frequently asked questions