Researchers have found “environmentally damaging” levels of illegal drugs in a river running through the Glastonbury Festival thanks to revelers publicly urinating, a new study has found. The researchers at Bangor University in Wales determined that concentrations of MDMA in the water quadrupled the week after the 2019 festival, which was attended by more than 200,000 people. Cocaine concentrations had reached a threshold previously shown to harm critically endangered European eels, which live in the river.

The lead scientist on the study, Christian Dunn, told CNN that though the levels were high, they declined “pretty quickly after Glastonbury [had] finished.” He added that the study drove home a reason to halt public urination, calling it a “pollutant” that “we’re only now really just becoming aware of.” Dunn suggested treatment wetlands and reed bed systems as solutions to filter out these kinds of pollutants, but reasserted the need to tell festival goers, “‘Look, another reason why you should not be peeing on the ground. Go and use the loos.’”