But other fish, like sturgeon prefer slower murkier water. Frogs, amphibians, birds, and small fish, in turn, eat these small animals. Larger fish and larger birds eat the frogs, amphibians, and small fish, and finally, larger animals such as alligators , crocodiles, as well as land-based animals such as wolves, bears , and eagles sit at the top of the food web. For instance, some plants anchor themselves along rocks and logs on the bottom of a slower moving river, some grow along the riverbank, and some float on top of the water with their roots hanging below. Animals develop special strategies to find the food they need and live in their own special niches formed by the plants and the river.
Some animals are active hunters, like salmon , pike, and otters .
Others, like crayfish, turtles, and even clams, are scavengers, cleaning up extra food that others leave behind. Some rivers in the uplands, or mountain areas, flow very quickly over steep, rocky terrain with many waterfalls and rapids. These types of rivers don't have much sediment on the bottom of their channel for many plants to find a place to anchor. But even these streams have nooks and crannies where moss and algae can grow. The favorite inhabitants of these streams are trout , who love cool, fast-running water.