The Pasig River connects the Laguna de Bay to the Manila Bay. This river is not used to transport commerce or anything anymore and is considered dead because of the bad pollution.
Life is unable to sustain in this river. However, the Philippines and many Green organizations are determined to clean up the river and make it sustainable to life. You should not plan a day swimming in the river. There are 13 bridges which cross the Pasig River, as well as the transit railways.
There are many landmarks and historical events which have occurred along the Pasig River. You can see the Malacanang Palace on the north bank, an orphanage on the island and on the south bank is the Sta. Ana Racetrack.