Disturbing images have revealed neon yellow water sitting stagnant in a lengthy section of river.
The alarming sight was captured in a series of photos of the Polmadie Burn in Glasgow, Scotland, on April 22 by a frustrated local.
Hundreds expressed their outrage after the photos were shared to Facebook, with locals labelling the occurrence "atrocious" and "very harmful".
Many weighed in with suggestions on what could have caused the water to turn neon yellow, with one speculating it was the result of an "algal bloom" and another saying it could be "non-harmful dye to track the flow of the water".
The true cause of the discolouration has since been revealed to be toxic waste from the nearby Shawfield Chemical Works, according to Glasgow Live. The plant shut down in 1967.
The reason for the colour is believed to be chromium-VI — a human carcinogen which can cause people to be at higher risk of developing lung cancer, according to the US Environmental Protection Agency (EPA).
There is reportedly growing concern the toxic waste, which has flown into the River Clyde - the second longest river in Scotland, could be causing serious harm to the health of those living in the area.
Residents pleaded with authorities to act fast when the discolouration intensified at the beginning of the year, the publication reported.
Locals thought weather patterns or local construction may have worsened the problem, with the river first turning green in February 2018.
The new photos have only added to their concern, with residents pleading with others to keep reporting the issue to the Scottish Environment Protection Agency (SEPA).
Local regeneration project Clyde Gateway has reportedly been working with the Glasgow City Council on diverting an underground culvert away from the area of pollution and ground remediation, the publication reported.
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