Vast numbers of dead fish have been hauled out of the Rodrigo de Freitas Lagoon in Rio de Janeiro over the last couple of weeks, and authorities are pretty sure they haven't died of excitement about the Olympic rowing and canoeing events to be held there next year. Dozens of workers have now retrieved more than 50 tons of fish, and while authorities blame the die-off on a change in temperature, an associate professor of aquatic ecology at a Rio university tells NPR that the lagoon is "stressed" and algal blooms have made it increasingly toxic. She says that while it may be safe—but stinky—to row in, falling in would be bad news.
Other scientists say the shortage of oxygen killing off the fish, from a small species called twaite shad, is caused by sewage and chemicals that end up in the lagoon, the BBC reports. Guanabara Bay, where the sailing and windsurfing events will be held, also has major environmental issues, including super-bacteria, and Brazilian authorities have admitted they won't be able to finish the cleanup in time for the 2016 Games. Rio Mayor Eduardo Paes tells NPR that he'd swim in Guanabara Bay's murky waters any time, though he doesn't say whether he would do the same in the lagoon where workers are still cleaning up dead fish. (Guanabara Bay has the added hazard of floating corpses.)