Fluorescent green goo was seen oozing from sewers onto the streets of Manhattan last week, sowing confusion among New Yorkers and social media snoopers. There’s no need to call the Ghostbusters nor the Teenage Mutant Ninja Turtles, though. 

Images of the oddly bright liquid were near the World Trade Center in the Lower Manhattan area on November 2, 2023.

"There's literal green sludge bubbling up from the ground next to the World Trade Center right now," Dan Pantelo posted on X (formerly Twitter)

"Can anybody explain this or are just living in full blown Gotham rn," he added, referencing the urban dystopia from the Batman universe. 

Thankfully, there’s a perfectly reasonable explanation. As explained in the “Community Notes” below the post, it appears that the liquid is simply a tracing dye commonly used to track leaks within the water system. 

Scientists and engineers use tracer dye to track the movement of water – and it often creates confusion. Earlier in 2023, the shores of Los Peñasquitos Lagoon in California turned a vibrant pink color, no doubt confusing some surfers.

It turned out that this was part of an experiment by UC San Diego’s Scripps Institution of Oceanography and the University of Washington to understand how freshwater outflows mix with the ocean surf zone. Despite its unnatural coloring, the dye was perfectly non-toxic and posed no risk to marine life. 

In other instances, odd-colored water might be a sign that something is awry. Back in 2017, residents of a snoozy Canadian town called Onoway woke up to find their tap water was hot pink. It was caused by a common water treatment chemical named potassium permanganate, which is used to extract smelly and dangerous hydrogen sulfide from the water. Unfortunately, a faulty valve caused higher concentrations of the chemical to enter into the main water supply.

Residents of New York should not be alarmed about the green liquid flowing down their sidewalks as tracer dye. However, we still wouldn’t recommend drinking water from a downtown gutter.