Summary:
- The article discusses the alarming decline of freshwater fish populations, particularly the collapse of one of Earth's greatest animal migrations - the spawning runs of salmon in the Pacific Northwest.
- Factors contributing to this decline include dams, climate change, habitat loss, and overfishing, which have disrupted the natural life cycle and migration patterns of these fish.
- The article emphasizes the importance of these fish migrations to the ecosystem, as they provide a crucial food source for other wildlife and play a vital role in the nutrient cycling of the rivers and forests they inhabit.