3. Mantanza-Riachuelo River, Argentina Originating in the capital city of Argentina, Buenos Aires, and empties into the Rio de la Plata, this river is known as the “slaughter creek” in English. It is 64 km long and defines the southern boundary of Buenos Aires federal district. This is a foul smelling river filled with toxic substances released from the household and industrial wastes. Millions of chemical wastes are being discharged in the water by petroleum companies resulting into water pollution.