Pollutants such as effluent wastewater, pesticides and pharmaceuticals in rivers are suspected to cause the intersex condition in fish, in which reproductive tissues are mismatched: most often, female germ cells are present in the testes.
To assess the incidence of the condition in river fish throughout the United States, Jo Ellen Hinck, a US Geological Survey scientist in Columbia, Missouri, and her team sampled 111 sites spread across the country. Intersex fish were found in 31% of the sites, with the greatest prevalence in the south-east. Small and largemouth bass were the species most commonly affected.
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Aquatic toxicology: Mixed-up fish. Nature 461, 451 (2009). https://doi.org/10.1038/461451e
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DOI: https://doi.org/10.1038/461451e
