8. Marilao River, Philippines Marilao river starts from the uplands of Rizal and flows through the Metro of Manila, in the Philippines. This river water is the most polluted, arousing a great concern not only to the government of Philippines but also the whole world. Various non-recyclable objects such as plastic, bottles, polythene bags and all other junks come from the leather tanneries, gold refineries and other industries. Also, toxic substances such as manganese, zinc, nickel and cadmium are found mixed with river's underground water making it undrinkable. Such toxicity made the river polluted and dangerous