In the last two weeks, tons of dead fish have floated to the surface of the Tiber, the famed Italian river that was once one of the lifelines of the Roman Empire. According to environmentalists, two-thirds of the fauna in a three-mile stretch of the river have been wiped out since July 15; even eels, the hardiest residents of the Tiber, have leapt onto the river’s banks to escape the water. City magistrates in Rome investigating the problem say it was caused by heavy rains earlier this month that flushed sewage, nitrates, and other pollutants down the Tiber. These pollutants led to a sudden boom in the algae population, which, the theory goes, sap oxygen from the water and cause the fish to choke to death. The magistrates claim there are no poisons, pesticides, or other toxic substances present in the river, but other city officials and environmentalists disagree and believe that the source of the problem is the Aniene, a badly polluted tributary of the Tiber.