In 2011, vast amounts of bacteria of the genus Vibrio – the culprit behind cholera – were identified in Rio de Janeiro’s Guanabara Bay and they are believed to be one of the causes behind the die-off of fish three years later. Toxins released by algal blooms in the bay’s polluted waters were likely another contributing factor. Covering an area of 384 square kilometers, Guanabara is the second largest bay along the Brazilian coast and its shores are surrounded by an urban area home to 16 million people. The bay is a caldron of disease-causing microorganisms that come from untreated household, hospital, and industrial waste dumped by 16 municipalities, according to a survey by scientists from universities and research centers in Rio de Janeiro, Brasilia, and the Netherlands (Frontiers in Microbiology, November 2015). Antibiotic-resistant genes have also been found in microorganisms in the bay. The authors of the study noted that the environmental degradation of the bay began with Brazil’s process of industrialization in the 1930s. They advise that the pollution abatement plan – stepped up because of the Olympic Games scheduled for this year – might raise water quality levels back to around 80% purity, as long as all of the domestic and industrial waste currently being dumped in the bay is treated. Today’s water quality would be even worse were it not for the ocean currents that wash into Guanabara and dilute the pollution. But the bay’s narrow entrance and its tidal and wind patterns limit the impact of the incoming sea water, and it takes an average of eleven days to renew half of the water in the Guanabara.