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Why sewage pollution is becoming an ecological issue
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Clean water is something most of us rarely think twice about - we turn on the tap, swim in lakes, or walk along beaches without wondering what might be lurking beneath the surface. But mounting evidence is forcing us to confront a murkier reality: our rivers, seas, and waterways are increasingly being polluted by untreated sewage.
Years of underinvestment, aging infrastructure, and weakened regulation have pushed sewage systems to breaking point, and in countries like the US, the consequences are becoming impossible to ignore. From closed beaches to foul-smelling rivers, the impact is now visible to communities across the country.
“ Underfunding and deregulation have pushed sewage systems to crisis point, and now countries such as the US are faced with the challenge of cleaning up their act and preventing their bodies of water from deteriorating even further. ”
In this article, we’ll explore why sewage pollution is such a growing concern and what’s behind the problem.
What is sewage, and how is it treated?
Sewage is any wastewater that comes from households, businesses, and industries. This includes everything from toilet flushes and sink water to wastewater from showers, washing machines, and dishwashers. In many areas, especially those with combined sewer systems, surface water - including rainwater runoff from roads and gutters - is also channelled into the sewage system, carrying oil, litter, heavy metals, and other contaminants.
“ Sewage contains a mix of organic matter, chemicals, nutrients, and harmful pathogens. If it isn’t properly treated, it can cause serious harm to aquatic ecosystems, spread disease, and make water unsafe for recreation or consumption. ”
The sewage treatment process
In most urban areas, sewage from homes and businesses is carried through a public foul sewer to a sewage treatment plant, also referred to as a sewage treatment works, where it undergoes a series of treatment stages before being discharged into the environment. The process is designed to remove waste products, reduce organic pollution, and eliminate harmful microbes:
Step 1: Preliminary treatment Solid matter like sanitary products, cotton buds, plastics, wipes, and debris are screened out to prevent damage to machinery and reduce blockages.
Step 2: Primary treatment The wastewater is held in settling tanks (also known as settlement tanks), where heavier solids (like food waste) sink to the bottom (forming sludge) and lighter materials like oils and grease float to the top and are skimmed off.
Step 3: Secondary treatment Also known as the biological stage of treatment, this process uses bacteria and microorganisms to break down dissolved and suspended organic matter. It’s often carried out in aeration tanks that supply oxygen to encourage microbial activity.
Step 4: Tertiary treatment This final stage focuses on removing contaminants that earlier stages may have missed, including nutrients like nitrogen and phosphorus, which contribute to algal blooms, as well as harmful pathogens. Techniques often involve filtration, UV disinfection, or chemical treatment.
In rural areas without access to the mains sewer (the public sewer system), individual properties often rely on septic tanks. These are small-scale systems that separate solids from liquids and allow partial treatment on site. However, without regular maintenance or proper siting, septic tanks can leak pollutants into the surrounding soil and groundwater.
After treatment, the leftover sludge from the primary and secondary stages undergoes further treatment to make it safe for disposal or reuse. Depending on the facility, it may be digested, composted, incinerated, used as fertilizer in agriculture, or sent to landfill.
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What causes sewage pollution?
Water pollution from sewage doesn’t happen by accident, it’s the result of outdated infrastructure, limited oversight, and a chronic lack of investment. In many parts of the world, untreated or poorly treated sewage is discharged directly into rivers, lakes, and seas, harming ecosystems and putting public health at risk.
Did you know? Over 80% of global wastewater is released into the environment without adequate treatment, according to UN Water.
Here are the key reasons why sewage pollution continues to be such a widespread problem:
1. Outdated and overburdened infrastructure
Many sewage systems still rely on ageing networks of pipes and drains built in the 19th or early 20th century, long before current population sizes and urban expansion.
In the UK, for example, much of the sewage infrastructure dates back to the Victorian era.
These older systems often combine wastewater and stormwater in the same pipes, known as combined sewer systems. During heavy rainfall, they quickly become overwhelmed and are forced to discharge excess sewage into nearby rivers or seas to prevent urban flooding — something referred to as combined sewer overflows (CSOs).
Without major upgrades or system separation, many countries are stuck with systems that simply cannot cope with today’s demands.
2. Inadequate or missing sewage treatment
Even where sewer networks exist, many sewage treatment plants are poorly maintained, under-capacity, or simply non-existent:
- In some regions, especially in low-income countries, there may be no centralized sewage treatment works at all.
- In others, treatment facilities may exist but are not functioning properly due to poor maintenance or lack of staff and funding.
- During peak usage or after storms, many facilities are forced to bypass treatment stages, discharging raw or partially treated sewage into natural water bodies.
According to the World Health Organization, around 46% of the global population lacks access to safely managed sanitation systems.
3. Dumping from ships and cruise liners
Sewage pollution isn’t just a land-based problem. Maritime sewage dumping is a major contributor to coastal water contamination.
While international regulations (like MARPOL Annex IV) prohibit sewage discharge within a certain distance from shore, enforcement is patchy, especially in waters where oversight is limited.
Cruise ships, in particular, are a major source. With an estimated 20 million people sailing annually, these vessels generate over 11 billion litres of sewage each year — not all of which is properly treated before discharge.
4. Underfunding and lack of political priority
Sanitation infrastructure is rarely a headline-grabbing issue and often falls by the wayside when it comes to government budgets and environmental priorities.
In the United States, for example, only $6 million was allocated between 2005 and 2019 to deal specifically with ocean-based sewage pollution.
In many countries, funds are diverted to more visible environmental challenges, like plastic waste or air pollution — despite the public health and ecological risks posed by untreated sewage.
Without sustained political will and financial support, the problem continues to fester.
5. Gaps in scientific research
Finally, sewage pollution has long been under-researched compared to other environmental threats.
While the effects of plastic pollution and oil spills are well documented, the long-term ecological impacts of sewage — such as hormonal disruption, oxygen depletion, and microbial resistance — have not been studied in the same depth.
This lack of data makes it harder to raise awareness, secure funding, or make better policy decisions.
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What are the major impacts of sewage pollution?
Sewage pollution has far-reaching consequences that go well beyond unpleasant smells and murky waters. From triggering harmful algal blooms to contaminating food chains and spreading disease, the discharge of untreated or poorly treated wastewater into natural ecosystems can devastate both the environment and the communities that depend on it.
Environmental damage:
“ Sewage introduces a toxic mix of contaminants into natural ecosystems, and even in small amounts, this can lead to negative impacts on water quality, biodiversity, and food chains. ”
1. Eutrophication and algal blooms
One of the most immediate environmental effects of sewage pollution is eutrophication — the excessive buildup of nutrients in a water body, particularly nitrogen and phosphorus. These nutrients stimulate rapid algae and plant growth, often leading to what are known as algal blooms.
When algae grow in dense layers on the water’s surface, they block out sunlight, suffocating the aquatic plants below. As these plants and algae die, they are broken down by bacteria — a process that consumes large amounts of oxygen.
The resulting oxygen depletion (hypoxia) creates “dead zones” where fish, invertebrates, and other aquatic life can no longer survive.
Some algal blooms, such as those caused by cyanobacteria (blue-green algae), also produce toxins that are dangerous to fish, birds, domestic animals, and even humans.
2. Disruption of aquatic food chains
Freshwater insects, which play a critical role in river and stream ecosystems, are particularly sensitive to low oxygen levels. Their decline can ripple through the food web:
- Fish species that rely on insects for food may starve or migrate elsewhere.
- Bird species that feed on aquatic life may also be affected.
- In extreme cases, the entire food chain can collapse, leaving a degraded ecosystem behind.
3. Vulnerability of sensitive habitats
Some ecosystems are especially susceptible to the contaminants found in sewage:
- Coral reefs can be smothered by algal growth and weakened by nutrient imbalances, leaving them more vulnerable to bleaching and disease.
- Mangroves and salt marshes — key coastal buffer zones — may suffer reduced biodiversity and productivity.
- Estuaries, where rivers meet the sea, are often hotspots for sewage discharge and can experience long-term degradation if pollution is persistent.
These ecosystems are not only biologically rich, they also provide vital services like coastal protection, carbon storage, and water filtration. Their loss has knock-on effects for both nature and people.
Chemical contamination and disease
Sewage doesn’t just contain organic waste. It also carries a cocktail of industrial and household chemicals, pharmaceutical residues, and pathogens:
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Chemicals like pesticides, herbicides, paints, solvents, and heavy metals can accumulate in sediments and aquatic organisms, working their way up the food chain.
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Hormones and medications flushed from homes and hospitals can interfere with fish reproductive systems and disrupt endocrine processes in wildlife.
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Pathogens present in human waste (including E. coli, salmonella, and viruses) can pose serious health risks.
In areas where untreated sewage enters water supplies used for drinking, bathing, or agriculture, the consequences can be deadly.
“ According to the World Health Organization, over 3.4 million people die every year from waterborne diseases such as cholera, dysentery, hepatitis A, typhoid, and polio, many of which are directly linked to sewage contamination. ”
Impact on coastal regions and vulnerable communities
The effects of sewage pollution are not evenly distributed. Coastal communities, river-based settlements, and low-income regions often bear the brunt of the problem:
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Local fisheries may collapse due to ecosystem disruption, cutting off both food and income sources.
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Tourism-dependent economies suffer when beaches are closed or water quality deteriorates.
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Poorer communities may lack the resources to build proper sanitation systems or clean up polluted environments, leaving them exposed to long-term health and economic hardship.
These communities are often excluded from decision-making and receive little support in addressing the root causes of pollution. As a result, sewage pollution not only becomes an environmental issue, but it's also a question of environmental justice.
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Where is sewage pollution a problem?
Sewage pollution is a global issue, but it’s often most severe in regions without adequate sanitation infrastructure. In many developing countries, large volumes of wastewater are discharged untreated into rivers, lakes, and coastal waters due to limited funding, rapid urbanization, and lack of access to modern sewage systems.
According to the UN, in some of the world's least developed countries, over 95% of wastewater is released into the environment without any treatment. In India, for example, less than 30% of sewage generated in urban areas is effectively treated, leading to widespread contamination of rivers like the Ganges. Similarly, in Nigeria, only 5.3% of urban households are connected to a sewer system, posing a risk to human health and contributing to high levels of waterborne disease.
“ But sewage pollution isn’t just a problem in the Global South. In recent years, countries like the United States, the United Kingdom, Germany, and France have also come under pressure for failing to curb illegal or unregulated sewage discharges, often due to aging infrastructure and regulatory gaps. ”
Why is sewage pollution a problem in the United States?
The United States faces significant challenges when it comes to sewage pollution. Ageing infrastructure, regulatory loopholes, and chronic underinvestment have left many communities vulnerable to overflows and water contamination, particularly during storms or flooding.
“ The U.S. Environmental Protection Agency (EPA) estimates that over 850 billion gallons of untreated sewage are discharged into American waterways each year. These overflows contaminate rivers, lakes, and coastal areas, often making them unsafe for swimming, fishing, or drinking. ”
1. A crumbling system
Much of the U.S. sewage infrastructure is decades, or even more than a century, old. Many cities, including New York, Chicago, and Washington, D.C., rely on combined sewer systems, which collect both wastewater and stormwater in a single pipe.
These systems are particularly vulnerable to heavy rainfall: when they become overwhelmed, they discharge untreated sewage directly into nearby water bodies.
The problem is especially severe in the Northeast and Great Lakes regions, where some cities experience hundreds of overflow events per year. For example, Detroit’s sewer system has reported regular overflows into the Detroit and Rouge Rivers, while Pittsburgh and Cincinnati are under federal orders to reduce overflow events that have polluted the Ohio River basin.
2. Unequal impact
The impacts of sewage pollution are not evenly distributed. Low-income communities and communities of color are more likely to be located near polluted waterways or ageing infrastructure.
A 2021 analysis by the Natural Resources Defense Council (NRDC) found that many of the worst sewage overflows and drinking water violations occur in areas that have historically been underfunded and excluded from infrastructure upgrades.
This raises concerns around environmental justice, particularly as climate change increases rainfall intensity and aging systems struggle to cope.
3. Policy and funding gaps
While federal law, under the Clean Water Act, prohibits the discharge of untreated sewage, regulatory exceptions still allow overflow discharges during storms. Enforcement is inconsistent, and many municipalities struggle to comply due to the sheer cost of upgrading systems.
The EPA’s Clean Water State Revolving Fund (CWSRF) provides financing for wastewater infrastructure, but demand far outstrips supply. The EPA estimated that the U.S. needs more than $271 billion in wastewater infrastructure investment over the next 20 years.
What’s being done to improve water quality?
There have been steps forward. The Bipartisan Infrastructure Law, signed in 2021, allocated $50 billion for water infrastructure, including $12.7 billion for clean water projects through the CWSRF. Some cities, including Philadelphia and Portland, have launched innovative "green infrastructure" programmes that use permeable surfaces and rain gardens to reduce stormwater pressure on sewage systems.
However, the scale of the problem remains vast. Without a coordinated, long-term investment strategy, many U.S. communities will continue to face the risk of sewage pollution and the environmental and public health consequences that come with it.
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Looking forward
Sewage pollution is a serious and often overlooked environmental issue, affecting not just low-income countries, but wealthy nations as well. In places like the US, decades of underinvestment, weak regulation, and prioritization of profits have left systems unable to cope.
Unlike plastic or air pollution, sewage rarely dominates headlines, yet its impact on ecosystems and public health is significant. The growing public backlash is now forcing governments and regulators to respond through stronger oversight, infrastructure upgrades, and greater transparency.
It’s a long overdue shift, and one that’s essential to protect the future of our rivers, seas, and the communities that depend on them.
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