What are the predators and preys in the rivers?

The predators and preys in the river based on the rivers food chain. In other means predators are those who eat other animals and creatures that live in the river and along the coast of the river. Preys are the ones to be eaten. eg: A crocodile salmons and salmons eats frogs eggs and frogs feeds on grass and other tiny things. NB: that is just an example