Hormones from human pharmaceuticals are entering waterways, with surprisingly powerful effects on fish populations. Synthetic hormones, particularly estrogen compounds from birth control pills and hormone replacement therapies, have become common in wastewater and runoff, disrupting aquatic ecosystems.

These hormones, along with other endocrine-disrupting chemicals from personal care products and agricultural sources, mimic the natural estrogens found in fish. When male fish are exposed to these chemicals, they sometimes develop intersex characteristics—such as producing eggs in their testes—or experience changes in reproductive behavior and fertility. The synthetic estrogens specifically impact species like bass and carp, making it harder for them to reproduce successfully, which in turn affects fish populations and the broader aquatic ecosystem.

As more research emerges, scientists are uncovering how these hormone-based changes affect not only the fish but also the food chains and biodiversity in affected water systems. Efforts to improve wastewater treatment and prevent pharmaceuticals from reaching natural waters are ongoing, highlighting the need for a balanced relationship between human health and environmental health.