Marikina River

The Marikina River (Tagalog: Ilog Marikina) is a waterway in eastern Metro Manila, Philippines. It is the largest tributary of the Pasig River, with headwaters in the Sierra Madre Mountains in what was known as Montalban, presently the municipality of Rodriguez, Rizal.

The Marikina River used to be an important transport route during the Spanish colonial era, but its importance as a transport route diminished when the Philippines' national highway system became more established. The resulting lack of river boat traffic and the deforestation of the upland areas in what is now the Upper Marikina River Basin Protected Landscape (UMRBPL) contributed to the river's siltation, further reducing its value as a transport route.

In the Pamitinan Protected Landscape located in Sitio Wawa, Brgy. San Rafael, in Rodriguez, the Marikina River is dammed by Wawa Dam, a structure built during the early 1900s to provide water for Manila. From Rodriguez, the river flows through San Mateo then to its namesake city of Marikina. In Pasig, the river meets the gates of the Manggahan Floodway, a controlled waterway used to prevent flooding in Manila during heavy rains by diverting most of the water of the Marikina towards Laguna de Bay instead of the Pasig River. Located 6.75 kilometers (4.19 mi) downstream is the confluence of the Marikina and Pasig rivers.

The river's depth ranges from 3 to 21 meters (9.8 to 68.9 ft) and spans from 70 to 120 meters (230 to 390 ft). It has a total area of nearly 75.2 hectares (0.752 km²) and is 27 kilometers (17 mi) long.The riverbank has an elevation of 8 meters above sea level at the boundary of San Mateo and Marikina. This slowly falls to an elevation of around 4 meters (13 ft) before the Malanday and Santo Niño boundary. The lowest elevation is along Calumpang which is 2 meters (6 ft 7 in) above sea level.

The Marikina River has a number of tributaries in the form of creeks and rivers, and at least one former river-section in Marikina's Barangay Tumana from which the original flow of the river has been diverted. These tributaries drain four municipalities and one city in the province of Rizal, and three cities in the Philippines' National Capital Region.

The biggest of these tributaries are upstream in the more mountainous areas of Rodriguez. This includes the Tayabasan River and Montalban River, the Boso Boso River, and the Wawa River, which meets the Marikina River just upstream of Wawa Dam. Further downstream from the dam, but still in the town of Rodriguez are the Puray River (which flows near Avilon Zoo) and Manga River.

Until this point the river follows a more or less east–west direction until San Jose, Rodriguez, where it takes a sharp north–south turn towards the municipality of San Mateo, where the Ampid River forms the boundary between Barangays Maly and Ampid. At this point across the river in Quezon City, Calamiong Creek drains Barangay Bagong Silang. Further downstream the Nangka River and its own tributary in the Sapang Labo Creek mark the boundary between San Mateo and Marikina.

Somewhere north of Brgy. Tumana in Marikina marks a point at which an American Colonial Era levee shifted the flow of Marikina River west, away from the population center of Sitio Bayanbayanan (now known as Concepcion Uno), where erosion had been a problem. The construction of a levee left behind a remnant waterway now known as Patay na Ilog (literally "Dead River", referring to the former path of the river) where the original path of the river once traversed, which rejoins the Marikina River just south of Tumana Bridge. The dredging for this American era levee left behind a large stone outcropping just below water level where the Marikina's children would play, back when the water was still clean, such that this part of the river is still called luksong kabayo.