Marikina River

The **Marikina River** is a waterway in eastern Metro Manila, Philippines. It is the largest tributary of the Pasig River, with headwaters in the Sierra Madre mountain range in what was known as **Montalban**, presently the municipality of Rodriguez, Rizal.

The Marikina River was an important transport route during the Spanish colonial era, but its importance as a transport route was diminished at the onset of the Philippines' national highway system. The dearth of river boat traffic and deforestation of the upland areas in what is now the Upper Marikina River Basin Protected Landscape (UMRBPL) contributed to the river's siltation, which reduced its value as a transport route.

## The Marikina River system

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 lake instead of the Pasig River. Located  downstream is the confluence of the Marikina and Pasig rivers.

The river's depth ranges from  and spans from . It has a total area of nearly  and is  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  before the Malanday and Santo Niño boundary. The lowest elevation is along Calumpang which  above sea level.

## Ecology

Due to neglect and uncontrolled industrial waste, rising pollution of the river had caused alarm that national and local administrations seek to repair. The Marikina River is on a verge of ecological imbalance as a strange species of fish has dominated its ecosystem. Since the late 1990s, the Marikina River has been dwelt by janitor fish. Before, the river was thriving with the local species _martiniko_, _ayungin_ and _biya_.

The growing fish population had prompted the city government to launch a new program to control their number. The city issued _Ordinance 004, series of 2007_, launching the _Janitor Fish Eradication Drive_ in the city of Marikina, granting cash incentives to participants, appropriating  annually for this purpose.

A scientific study of the species found in five locations in the Laguna de Bay tributary system, including the Marikina River, revealed that the specimen of janitor fish previously reported as _Hypostomus plecostomus_ actually belongs to the genus _Pterygoplichthys_, family Loricariidae. The collected specimens for this study consisted of two species: _Pterygoplichthys disjunctivus_ and _Pterygoplichthys pardalis_. Both species were collected from the Marikina River. Only the species _disjunctivus_ was collected from the Pasig River.

## Infobox (mapframe)

- **wikidata**: yes
- **zoom**: 10
- **height**: 250
- **stroke-width**: 1.5


## Infobox (river)

- **name**: Marikina River
- **image**: Marikina River from Riverbanks Center, Dec 2023.jpg
- **image caption**: Marikina River in Marikina
- **map**: Pasig-marikina river drainagebasin.png
- **map caption**: drainage basin, Drainage map of the Pasig River, Pasig-Marikina River River system
- **pushpin map**: Luzon mainland#Philippines
- **pushpin map caption**: Marikina River river mouth, mouth
- **subdivision type1**: Country
- **subdivision name1**: Philippines
- **subdivision type2**: Region
- **source1**: Sierra Madre (Philippines), Sierra Madre mountains
- **source1 location**: Rodriguez, Rizal
- **mouth**: Pasig River
- **mouth location**: Pasig
- **progression**: Marikina–Pasig