The Pasig River (Filipino: Ilog Pasig, Spanish: Río Pásig), is a river in the Philippines that connects Laguna de Bay to Manila Bay. Stretching for 25 kilometres (15.5 mi), it bisects the Philippine capital of Manila and its surrounding urban area into northern and southern halves. Its major tributaries are the Marikina River and San Juan River.

The Pasig River is technically a tidal estuary, as the flow direction depends upon the water level difference between Manila Bay and Laguna de Bay. During the dry season, the water level in Laguna de Bay is low with the river's flow direction dependent on the tides. During the wet season, when the water level of Laguna de Bay is high, the flow is reversed towards Manila Bay.

The Pasig River used to be an important transport route and source of water for Spanish Manila. Due to negligence and industrial development, the river has become very polluted and is considered dead (i.e., unable to sustain life) by ecologists. The Pasig River Rehabilitation Commission (PRRC), which was established to oversee rehabilitation efforts for the river, is supported by private sector organisations such as the Clean and Green Foundation, Inc. that introduced the Piso para sa Pasig (Filipino: "A peso for the Pasig") campaign in the 1990s.

Pasig is a city in the Philippines which was the former provincial capital of the province of Rizal prior to the formation of Metro Manila, the National Capital Region of the country of which it became a part. Located along the eastern border of Metro Manila, Pasig is bordered on the west by Quezon City and Mandaluyong; to the north by Marikina; to the south by Makati, Pateros, and Taguig; and to the east by Antipolo, the municipality of Cainta and Taytay in the province of Rizal.

A formerly rural settlement, Pasig is primarily residential and industrial, but has been becoming increasingly commercial in recent years, particularly after the construction of the Ortigas Center business district in its west. The city is also the see of the Roman Catholic Diocese of Pasig, making its cathedral (formerly the Immaculate Conception Cathedral) a landmark built around the same time as the town's foundation in 1573.

Etymology

The city's name Pasig was believed to have come from the old Sanskrit word “passid”, or "sand", which refers to the tribal community beside the sandy edges of the river. Some historians believed that El Pasig came from "Legaspi" (Miguel Lopez de Legazpi, the Basque explorer well known for being involved in the "Sanduguan", and was the first Governor-General of the Spanish East Indies.