What Happens When Sewage Enters a River?

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Environmentalists and citizens alike worry when raw sewage discharges into rivers and streams. The presence of sewage presents a health hazard for humans, as well as fish and aquatic mammals. Sewage in rivers has long-lasting impacts on local water quality and general river ecosystem health.

Entry Methods

Sewage makes its way into rivers through both point source and non-point source routes. You can easily identify and remedy point source routes, such as eaky or misdirected pipes funnelling sewage into a river. Non-point source routes, such as water runoff from a neighbourhood, are harder to identify.

Most often, sewage gets into rivers during heavy rainstorms. Sewers can overflow or fill with water. When this happens, water and sewage mix and the resulting liquid drains into rivers and streams after the storm.


Raw sewage can make people and animals sick as it generally contains high levels of coliform bacteria. The most dangerous of the coliform bacteria, E. coli, exists almost exclusively in fecal matter. Scientists often do periodic water quality checks on major rivers -- if high levels of coliform bacteria are present, they will usually post signs warning people not to swim in or drink the water.

Effects on River

Other than the danger to human health, rivers which are contaminated with sewage change their ecological characteristics. Sewage is high in nitrogen and this excess of nitrogen in the water provides a feeding source for phytoplankton and algae.

An excess of phytoplankton or algae in the water is called eutrophication. The excess plankton makes the water cloudy and green. Furthermore, excessive algae and phytoplankton can deplete oxygen in the river, making it difficult for fish and underwater mammals to survive.


Finding point sources of sewage discharge and fixing or removing them is one easy way to prevent sewage from getting into our rivers. Additionally, one of the biggest reasons that water runoff can carry non-point source pollution is the large number of paved surfaces in our communities. Unpaved surfaces, like grass, soak up some of the water runoff from a storm, meaning that less of it gets to the rivers. By working to ensure that our communities have enough impermeable spaces like grass, gardens, fields and even dirt lots, we can ensure that less sewage will get into our rivers during major storm events.