Clearly a river cannot have legal rights. If the river bursts its banks and floods my house, can I sue the river? Clearly I cannot because how do I sue the river, who represents the river and how does the river have money to pay me? The river cannot appointment executives to represent its interests.

In reality the local government acts for the protection of the environment, so why pretend the river has rights? If you want cleaner rivers then pass legislation with appropriate level of punishment such as fines/prison.