In Herman Melville’s book Moby Dick, a character named Starbuck drowns when his ship is sunk by a monstrous whale. In today’s world, our own Starbuck(s) is still disappearing into the ocean, but while Melville’s unfortunate character didn’t leave a trace behind, our penchant for coffee, tea and energy drinks is leaving a surprising residue: caffeine.

Researchers from Portland State University found recently that human activity is polluting ocean waters with measureable amounts of caffeine.

Samples of water from the Pacific Ocean off the Oregon coast yielded surprisingly high levels of this contamination. The researchers initially believed that caffeine pollution was most likely to occur in areas near wastewater treatment plants, major population centers or where rivers and streams empty into the ocean.

They were surprised to find caffeine in the ocean in areas far from the predicted areas. This indicates that while wastewater plants may effectively remove many contaminants from water, septic tanks and sewer overflows still allow large amounts of the contaminants to be washed to sea.

“Our study findings indicate that, contrary to our prediction, the wastewater treatment plants are not a major source of caffeine to coastal waters,” says researcher Elise Granek. “However, onsite waste disposal systems may be a big contributor of contaminants to Oregon’s coastal ocean and need to be better studied to fully understand their contribution to pollution of ocean waters.”

Caffeine is a drug found in many beverages and pharmaceuticals consumed by humans. Its presence in the ocean means that other drugs consumed by humans could also be making it into the water.