Male fish are turning into females thanks to chemicals from birth control pills and makeup being flushed down drains, according to a new study.

The study of freshwater fish in Britain found a fifth of males are now showing feminine traits — including producing eggs, a reduced sperm count and less aggressive behavior — due to gender-bending chemicals found in the contraceptive pill, cleaning agents, plastics and cosmetics, the Telegraph reports.

“We are showing that some of these chemicals can have much wider health effects on fish [than] we expected,” the University of Exeter’s Professor Charles Tyler told the paper.

“Using specially created transgenic fish that allow us to see responses to these chemicals in the bodies of fish in real time, for example, we have shown that oestrogens found in some plastics affect the valves in the heart.”

And contraceptives aren’t the only human pills messing with marine life — previous studies have shown antidepressants in the water are also putting some pep in their paddle, he added.

“Other research has shown that many other chemicals that are discharged through sewage treatment works can affect fish, including antidepressant drugs that reduce the natural shyness of some fish species, including the way they react to predators,” Tyler said.