Ciprofloxacin, a frontline treatment for intestinal and urinary tract infections, surpassed the industry threshold at 51 of the sites tested.

At one location in Bangladesh, concentrations of another widely used antibiotic, metronidazole, were 300 times above the limit, the researchers said.

"The results are quite eye opening and worrying, demonstrating the widespread contamination of river systems around the world with antibiotic compounds," Alistair Boxall, a scientist at the York environmental Sustainability Institute, said in a statement.

The widespread presence of antibiotics not only impacts wildlife, but likely contributes to the problem of antimicrobial resistance.