There are several important river systems which have their sources on Pinatubo.
The major rivers are the Bucao, Santo Tomas, Maloma, Tanguay and Kileng rivers.
Before the 1991 eruption these rivers were important ecosysyems.
However the eruption filled many valleys with deep pyroclastic deposits.
Since the 1991 eruption, the rivers have been clogged with sediment