Complex sentence: The lake is recognised as the largest highly acidic crater lake in the world, and since it is also a source for the river Banyupahit, resulting in highly acidic and metal-polluted water, it has a significant detrimental effect on the downstream river ecosystem.
Split into simpler sentences: The lake is recognised as the largest highly acidic crater lake in the world. It is also a source for the river Banyupahit, resulting in highly acidic and metal-enriched river water which has a significant detrimental effect on the downstream river ecosystem.