It’s a Tuesday morning in the Xochimilco neighborhood of southern Mexico City, a lively world heritage site known for its network of canals and floating gardens. On the weekends, the space is clogged with colorful party boats carrying drunken revelers and traveling mariachi bands but today, the murky green waterways are empty and eerily still. A lone vessel glides by, filled with Greenpeace volunteers wearing hazmat suits and ominous expressions.

Architect Elias Cattan, president of the architecture firm Taller 13, leans over the edge of the boat, dipping a small glass jar into the water. He seals it with a twist-on cap and examines the sample; tiny unidentifiable critters squirm amidst the sludgy liquid and neon algae disperses like flakes inside a snow globe. A few pieces of garbage sink to the bottom. “This is perfect,” Cattan tells Quartz. “The dirtier, the better.”

On the day Quartz visits, Cattan and his small army of environmentalists are collecting jars of dirty water from nearly a dozen different sources throughout the Mexico City metropolitan area. Eventually, Cattan’s team amassed more than 15,000 of these jars, which now form the structural backbone of a large-scale art installation.