why is the chicago river so blue

Why is the Chicago River so blue? The Chicago River is a famous waterway, and its brilliant blue color stands out against the city’s skyscrapers.

It definitely looks stunning, but it also makes people wonder, “Why is the colour of the Chicago River so blue?”

The blue color of the river is not as simple to explain as at first glance; it is the consequence of a complex interaction between natural and man-made elements.

The Chicago River is so blue because of a lack of sediment and algae, water treatment, and many other natural and artificial factors. 

Witnessing the Amazing Colors of Rivers

witnessing the amazing colors of rivers

The water in most rivers is clear, but when there is a lot of algae floating around, the river turns green.

Calcium carbonate turns water blue, whereas sulfur turns it red, and muck turns it black.

The river takes on new tones as a result of industrial pollution.

For instance, effluent with a high concentration of copper appears blue, while paper mill wastewater appears black.

It means that chemicals play a large role in coloring the riverbanks, rocks, and embankments.

But is that also the case with the Chicago River?

Fact: The Chicago River system spans over 251km and flows from Park City to Lockport. 

Why Is the Chicago River So Blue?

the blue mystery of chicago river

The Chicago River’s blue color looks stunning. Not only does this vibrant hue enhance the city’s aesthetic value, but also tends to attract curious onlookers.

But, why is that color really blue? Well, here are some possible explanations for this phenomenon. 

Depth and Clarity

Like any other body of water, the Chicago River takes its color mostly from its depth and clarity.

Bluer seas are created because shorter wavelengths of light, such as blue and violet, are reflected back by clearer waters.

depth and clarity

Since longer wavelengths (red, orange, and yellow) are absorbed readily, this reflection becomes stronger as water depth increases.

The blue color of the sky is the result of light being scattered and absorbed, a phenomenon known as Rayleigh scattering.

When it comes to the hue of the Chicago River, depth and clarity are key factors

An Important Consideration

The distinctive, often vivid blue color of the Chicago River is the result of a complex interplay between these natural processes and other environmental and man-made impacts.

This makes for a visually distinguishing feature of this historic waterway. 

Artificial Dye

artificial dye

One of the most well-known traditions in Chicago is the practice of coloring the river for important celebrations.

The most famous example of this is the dyeing of the river green for the annual St. Patrick’s Day festival, which is a major attraction for both locals and visitors.

The eco-friendly dye temporarily turns the river into a ribbon of emerald water, adding to the festive atmosphere of the entire city.

It is worth noting that the river’s signature blue tint is unaffected by the dyes used for the brief color shifts that occur during these episodes.

Because of their rapid and safe dissipation, the river’s natural blue hue returns within a few days.

And the artificial dyes, while contributing to the city’s vibrant cultural festivals, do not add to the river’s regular color and make it look even more blue after the festival. 

Sediment and Algae

sediment and algae

Sediments and algae blooms can drastically alter the color of any body of water.

Due to the light scattering properties of these natural components, water typically appears green or murky brown.

However, due to intensive cleanup efforts in recent years, these sediments and algae are much less prevalent in the Chicago River.

The city has reduced the frequency of algae blooms and the amount of silt in the river by cutting back on pollution.

Water purity has improved because of this massive environmental endeavor.

Because there are fewer particles in the water to absorb the blue light, the river’s signature color has become more pronounced.

There is a direct correlation between the river’s purity and its beautiful blue color

Reflection from the Sky

reflection from the sky

The sky’s reflection is a major contributor to the blue color of the Chicago River.

Due to their reflecting properties, bodies of water can take on the hue of the sky above them on bright, sunny days.

Because blue light travels in shorter, smaller waves than other hues, it is more easily scattered by molecules in Earth’s atmosphere, giving the sky its characteristic blue hue.

The Chicago River takes on the color blue when its calm, clean waters reflect the sky above.

In the middle of a busy city like Chicago, the color of the river stands out in vibrant contrast to the rest of the cityscape, making it one of the city’s most distinctive features. 

City Infrastructure and Riverwalk

city infrastructure and riverwalk

The beautiful blue color of the Chicago River is largely due to the city’s infrastructure, including the Riverwalk.

Concrete and pale stone are common in the city’s architecture, as are outdoor spaces like this crowded walkway beside the river.

Because of their high reflectivity, these materials are ideal for focusing sunlight on the river below.

And that is the reason why the river appears much bluer than before.

The cityscape thus not only serves to frame the Chicago River, but also enhances its particular blue attractiveness, providing a stark contrast to the surrounding countryside. 

Water Treatment

water treatment

The revitalization of the river and improvements to water quality have greatly contributed to the blue color of the Chicago River.

Over the past few decades, the river has undergone extensive cleanup and restoration work.

In order to lessen pollution and sedimentation, this has required extensive water treatment methods.

Meanwhile, efforts to bring back native wildlife have contributed to a healthier ecosystem.

The cumulative consequence of these efforts is a river that is cleaner and clearer, better reflecting the blue of the sky above.

Fact: The revitalization of the Chicago River is evidence of effective environmental management and municipal planning, as it amazingly winds through the city's core.  

What Besides Blue Color Makes the Chicago River Unique?

The Chicago River runs through the middle of the Windy City, making it unique.

The river’s vivid blue color stands out well against the cityscape of Chicago, making it a prominent landscape feature.

chicago river's unique attributes beyond color

But, its blue color is not the only factor making the Chicago River as popular as it is.

Let’s talk about some factors other than its blue color that make it truly spectacular:

Reversal of Its Flow

The reversing of the flow of the Chicago River is a unique engineering feat that sets the city apart.

One of the most audacious engineering feats of the twentieth century was the modification of the river’s flow.

Chicago’s drinking water used to come directly from the river’s original source: Lake Michigan.

Concerns over sanitation and the security of the city’s water supply, though, prompted a radical solution: reversing the river’s course.

The river’s original path led it into Lake Michigan, but engineers diverted it so it now flows into the Mississippi.

This change not only protected the city’s water supply, but also exemplified the potential of human intellect and engineering. 

Variety of Outdoor Activities

variety of outdoor activities

The Chicago River is more than simply a scenic landmark; it also serves as a lively gathering place for a variety of outdoor activities.

The Chicago Riverwalk, a long walkway that runs along the river’s edge, is a notable landmark.

It is a popular spot for strolls, runs, and even watercraft excursions.

Several great restaurants along the Riverwalk are perfect for enjoying a meal while taking in the scenery.

Fact: Chicago Riverwalk is an integral element of Chicago's social and cultural fabric and provides breathtaking, panoramic views of the city's architecture. 

Model of Excellence

model of excellence

When it comes to urban environmental restoration, the Chicago River is a model of excellence.

In recent years, the city has made significant strides in cleaning up the river, reducing pollution, and returning it to its natural state.

These coordinated efforts have restored the river’s environment, making it habitable once more for the local fauna.

The river is now not just a scenic part of the urban landscape, but also a thriving ecosystem.

Fact: The Chicago River is a symbol of environmental resilience in the midst of a bustling city and evidence of the possibility of harmony between urban development and nature. 


Why is the Chicago River so blue? Just like any other body of water, the scattering of light plays a big role in determining the color of the Chicago River.

Other than that, the lack of algae and sediment is another reason why the river looks so blue.

But interestingly, the blue color is not the only reason why people adore the Chicago River.

It is also considered a model of excellence in many other ways, and is definitely worth a visit.