How does the flow of acid rain into a river make the survival of aquatic life in a river difficult? (AS7)

The flow of acid rain into a river changes the pH of the river. The pH of the water decreases due to the acid rain which is not suitable for the survival of aquatic plants and animals.

They need pH of 7 to 8 for survival. But acid rain increases the acidity of the river due to which it becomes difficult for them to survive.