Each river stage provides a different habitat and ecosystem for its inhabitant fauna and flora. Most notably, water in young rivers are typically sourced from glaciers; therefore, rivers provide freshwater. Freshwater provides a habitat for aquatic animals that can only survive in freshwater. At the same time, glaciers have to be at a high elevation to exist.
As glaciers melt, waterfalls are formed. Waterfalls provide a faster flow of water, which is necessary for certain animals to survive, as faster flowing water is also colder than more still water. The end of the waterfall typically contains potholes as well. Potholes are holes that have been created by the erosion of bedrock. Animals such as tadpole shrimp take advantage of potholes and make them their permanent habitat and even lay their eggs there. An example of an existing young river is the Brazos River. The Brazos River contains a variety of fauna. Land mammals such as Whitetail deer, rabbits, and rodents are commonly found, while forty-four different species of fish including minnows and shiners are present.
At the same time, migratory waterfowl such as mallards and blue herons are existent, along with bald eagles that hunt the fish in the river. Various species of both venomous and non-venomous snakes including cottonmouths and rattlesnakes live near the Brazos River. Varieties of flora are also present in the Brazos River.
Plant life includes sycamores, buckeyes, yaupons, wild grape, oaks, and palmettoes are commonly found along the Brazos River. Mature rivers feature meanders. Meanders are series of curves in a river. These curves cause the water velocity to decrease, which then allows for more biodiversity. From this, aquatic and riparian habitats are able to develop. The Ohio River is an example of a mature river that contains a large biodiversity. Inhabitant fauna in the Ohio River comes in a large variety.
Most notably, in the riverbed are freshwater mussels. These mussels not only provide a habitat for invertebrates and fish, but they also provide food for other wildlife. Migratory birds such as waterfowls, songbirds, and osprey mate and hunt in the Ohio River. Within the meanders are various fish such as spotted bass, sauger, freshwater drum, and flathead catfish. At the same time, insects and amphibians including various species of dragonflies, butterflies, frogs, toads, and turtles live near the Ohio River. Meanwhile. Mammals such as deer and raccoons use the Ohio River as a source of water and food.
Meanders of the Ohio river also allow for diverse types of flora. The riparian and deciduous forests provide a habitat for a multitude of fauna near the Ohio River. The riverbed also allows for the creation of aquatic vegetation such as freshwater eelgrass.