Rivers have become both overfished and polluted. Gillnets now allow fishermen to kill huge amounts of fish at a time. They often use only the larger and more profitable fish, dumping the dead smaller fish and other animals such as dolphins back into the rivers. Pollution from mining has killed fish populations in the mighty Amazon River. Many indigenous people, who have depended on these fish for centuries, have become sick from the poisoned fish.
Extinction happens naturally.
Species like the dinosaurs and the saber-toothed tigers have died off from their failure to adapt to the changing environment. But nowadays humans are altering their habitats too quickly for them to adapt. Only in this modern day have so many species become extinct in such a short period of time. It would be a sad world indeed without the beauty of toucan or the grace and power of the jaguar. GILL NET a huge fishnet set vertically in the water so that all fish swimming into it become entangled by their gills.