Stream-side ecosystems and the biological, chemical, and physical characteristics of rivers are just a few of the many and diverse effects that big dams have on the environment.
Fish movements are impeded by the dam wall itself, which can in some circumstances and with some species totally divide spawning grounds from rearing habitats. Additionally, sediments trapped by the dam are essential for preserving physical processes and habitats downstream from the dam (include the maintenance of productive deltas, barrier islands, fertile floodplains and coastal wetlands).
The change from a naturally flowing river environment to an artificial slack-water reservoir habitat upstream of the dam is another big and evident effect. Changes in a reservoir's physical characteristics, chemical composition, dissolved oxygen levels, and temperature are frequently not suited for the aquatic plants.
Indeed, reservoirs frequently support invasive and non-native species (such as snails, algae, and predatory fish), which further jeopardise the natural plant and animal ecosystems along the river.
The most significant long-term environmental effects are frequently brought on by changes to a river's flow and sediment transport downstream of a dam. The timing and volume of a river's flow affect how life develops in and around it. Water flows that are disrupted or altered can cause just as much damage as entirely drying up river sections and the life that lives there. However, even little variations in water flow quantity and timing have an impact on aquatic and riparian species, which can disrupt the biological interdependence of a river system.