River struggling against pollution.

River Pollution Unveiled: How Urban Sewage Impacts Water Quality

Theo Raines in Climate & Environment December 2025 • 4 min read.

"Discover the hidden dangers of domestic waste on river ecosystems and what it means for our water resources."

Many cities still lack proper treatment for domestic sewage, leading to the introduction of a complex mixture of biodegradable organic substances and inorganic nutrients into aquatic environments. This pollution reduces water quality by affecting the physical and chemical properties of the water.

Rivers are the primary recipients of domestic sewage. When they receive volumes exceeding their natural purification capacity, physical and chemical modifications occur in the water, affecting the entire ecosystem along the watercourse. This includes increased proliferation of decomposing microorganisms and a reduction in dissolved oxygen levels, impacting aquatic life.

The Piracicaba, Capivari, and Jundiaí river basin, home to over 5 million people, suffers from significant eutrophication due to high levels of total phosphorus from domestic sewage. This study investigates the influence of organic sewage on the Camandocaia River, aiming to understand the extent of pollution from its sources to its mouth.

The Impact of Sewage on River Characteristics

The study examined the influence of domestic sewage on the water quality of the Camandocaia River by analyzing various limnological variables, including pH, turbidity, color, manganese, iron, dissolved oxygen, and total nitrogen and phosphorus. Water samples were collected from 12 points along the river, from its headwaters to its confluence with the Jaguari River. The data collected were analyzed using Principal Component Analysis to understand the major factors influencing water quality.

Here’s a breakdown of the key findings:

Oxygen Saturation: Oxygen saturation levels were generally good, staying above 70% at most points, except at Point 9 (38.8%).
Nitrogen Levels: The lowest nitrogen levels were detected at Points 1-3 (0.18 to 0.21 mg L-1), while the highest levels were at Points 9 and 10 (1.29 and 1.79 mg L-1).
Phosphorus Levels: The highest phosphorus concentration was found at Point 9 (345.5 µg L-1), exceeding acceptable limits.
Correlation Analysis: Most variables, except oxygen saturation, correlated positively with the first principal component. The two main components explained 86.6% of the total variance.

The results indicate that the Camandocaia River remains relatively unpolluted until it reaches Amparo. Pollution levels were highest at the end of Amparo, followed by a partial self-purification trend towards the Jaguari River confluence. However, even the most polluted point in the Camandocaia River showed lower pollution levels compared to other polluted rivers.

Protecting Our Rivers: A Call to Action

This study highlights the vulnerability of river ecosystems to urban sewage and the importance of effective wastewater treatment. The Camandocaia River, while showing some self-purification capacity, still suffers from significant pollution in certain areas, particularly near urban centers.

The findings emphasize the need for improved sewage treatment facilities and better management practices to protect water quality. Reducing the discharge of untreated sewage into rivers is crucial for maintaining healthy aquatic environments and safeguarding water resources for future generations.

By understanding the impacts of pollution and implementing effective solutions, we can work towards preserving the ecological integrity of our rivers and ensuring access to clean water for all.

About this Article -

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This article is based on research published under:

DOI-LINK: 10.4025/actascibiolsci.v34i2.6708, Alternate LINK

Title: Influência Do Despejo De Esgoto Doméstico Nas Características Limnológicas Do Rio Camandocaia, Bacia Hidrográfica Do Rio Piracicaba, Estado De São Paulo

Subject: General Agricultural and Biological Sciences

Journal: Acta Scientiarum. Biological Sciences

Publisher: Universidade Estadual de Maringa

Authors: André Alberto, Basílio Gomes Ribeiro Filho

Published: 2012-03-28

Everything You Need To Know

How does urban sewage affect the quality of river water?

Urban sewage introduces biodegradable organic substances and inorganic nutrients into rivers, leading to a decline in water quality. This degradation affects the physical and chemical properties of the water, impacting the entire ecosystem. The increased presence of these substances leads to proliferation of microorganisms that decompose the organic matter, further depleting dissolved oxygen levels, which is crucial for aquatic life. The study examined the influence of domestic sewage on the water quality of the Camandocaia River, focusing on variables like pH, turbidity, color, and levels of elements such as manganese, iron, nitrogen, and phosphorus.

What are the key impacts of sewage on river ecosystems?

The primary impact of domestic sewage on rivers is a reduction in water quality. This can manifest through several ways: Increased levels of pollutants like nitrogen and phosphorus, which can lead to eutrophication, a process where excessive nutrients fuel the overgrowth of algae and aquatic plants. This overgrowth can deplete oxygen levels as they decompose. The Camandocaia River study found that higher levels of nitrogen and phosphorus were concentrated near urban areas, showing the direct impact of sewage input. Oxygen saturation levels are also impacted, as seen in the Camandocaia River where levels dropped significantly at certain points due to sewage presence. The Piracicaba, Capivari, and Jundiaí river basin also suffers from eutrophication because of high phosphorus from sewage.

What is the self-purification process in rivers, and what are its limitations?

The self-purification process in rivers refers to the natural ability of a river to cleanse itself of pollutants. This process involves physical, chemical, and biological mechanisms that help break down and remove contaminants. However, this ability has limits, particularly when rivers receive excessive amounts of urban sewage. When the sewage volume exceeds the river's capacity to purify itself, the pollutants accumulate, leading to significant changes in water quality. The Camandocaia River demonstrates this: even with some self-purification, specific sections near urban centers still show high pollution levels.

What specific methods were used to analyze the impact of sewage on the Camandocaia River?

The Camandocaia River study investigated the impact of domestic sewage on the water quality using several limnological variables like pH, turbidity, and dissolved oxygen. These were measured at 12 different points along the river. The Principal Component Analysis was used to understand the major factors influencing the water quality. The results highlighted that the pollution levels were highest near urban areas, such as Amparo, and there was a partial self-purification trend towards the Jaguari River confluence. This study provided valuable insights into the specific effects of sewage on the river's health.

What is the overall significance of this research regarding river pollution?

The study's findings underscore the vulnerability of river ecosystems to pollution from urban sewage and the importance of effective wastewater treatment. It highlights the need to manage sewage and urban waste to protect water resources. The Camandocaia River, while demonstrating some self-purification, still shows significant pollution in certain areas. This emphasizes that implementing wastewater treatment is essential to prevent environmental degradation and to preserve the health of river ecosystems. Without proper treatment, rivers can become heavily polluted, affecting aquatic life and water quality, as seen in the study.