The paucity of commercial fish in the main rivers within the NCR is a direct result of
the level of pollution in these waterways. Most of the year there is insufficient
oxygen within the waterways to support anything but the coarsest fish species. In
the wet season, there is substantial diluting runoff which improves the river water
quality to such an extent that some fish can survive. The fish are not breeding in
commercial quantities in the river, but are just motile species moving from the
cleaner upper reaches of the Marikina River and Laguna Lake towards Manila Bay.
Residents living along the Pasig and Marikina Rivers catch some of these fish. The
health impacts of eating these fish has not been established by specific
epidemiological studies, but may be expected to have some chronic impacts given
the presence of persistent chemicals within the river systems