The Marilao River is part of the Marilao-Meycauayan-Obando (MMO) river system.

The MMO river system is 55 kilometers in length which traverses the cities of Caloocan, Valenzuela, and Malabon in Metro Manila and San Jose Del Monte in Bulacan  and the towns of Meycauayan, Marilao, Obando and Sta. Maria, also in Bulacan

The river system gained   notoriety in 2007 when Blacksmith Institute, a New York-based environmental watchdog,  called it one of the 30 most polluted areas in the world.

Then Secretary of the Department of Environment and Natural Resources (DENR), Lito Atienza, said it is an acknowledged fact that the MMO is “one of the most contaminated rivers in the country’’.  It has come to its polluted state over period of time due to the many different sources of pollution.

The rehabilitation of the Marilao-Meycauayan-Obando (MMO) river system started in  February 20, 2008 following Secretary Atienza’s declaration of the major waterway as a water quality management area.

The classification of MMO as a water quality management  area means the implementation of an integrated action program to ensure the rehabilitation of the water system.

“It is very timely and most appropriate that this river system be declared as a water quality management area. The declaration will inspire collective efforts that would synergize the river clean up of heavy metals and organic pollution,” Atienza said.

DENR is working in partnership with local government units (LGUs) in Bulacan, as well as other government agencies and private groups, “to restore the former glory of the MMO river system”.