A stream running along the outskirts of Buenos Aires in Argentina appears more like a river of blood after turning red in the span of hours.

Many residents were in shock this morning when they realized the Sarandí stream, located in the municipality of Avellaneda, was crimson red. The narrow river is a tributary of the Río de la Plata, which is an estuary bordering Argentina and Uruguay. It also runs along a ton of tanneries and other industries that use harsh chemicals, which many believe is the reason for the red color.

Once local authorities learned of the discolored water, they immediately began analyzing samples to determine the cause.

Buenos Aires River Turns Into ‘Stream of Blood’ As Officials Fear a Toxic Leak

One local resident named María Ducomls told The Associated Press that she recently woke to powerful odors in the air.

“At 5:30 a.m., we already had a special and hazardous waste incinerator spewing pollutants into the air,” she said. It wasn’t long before the stream below was crimson in color.

“It looks like a stream of blood,” she said. “We have never seen it like this.”

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A river near Argentina’s capital has turned blood red, alarming residents and prompting officials to investigate. #news

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According to the outlet, officials believe the stream might have the presence of aniline, a toxic substance and oily liquid used in dyes, rubber, medicines, and other products. After collecting water samples, the officials filed a complaint to hopefully mitigate the situation.

This unfortunately isn’t the first time something like this has happened in the Sarandí stream. In fact, its water often has an oily appearance and turns different colors, from gray to violet. However, the bright red has been especially alarming.