text: Large dams and the production of hydropower are an important part of today's energy supply and cover a broad part of river engineering. The approach of releasing small quantities of water through turbines responds to the growing power demand from rapidly growing cities; however, it also flattens the rivers hydrographs, and is responsible for a decline in seasonal hydraulic variability and for the loss of delta-building dynamics, as the sediments are stored in the reservoir. Small-scale users of the deltas lose the biodiversity and ecosystem productivity on which they depend.
  The aquatic ecosystem consists of a chain of organisms which are dependent on each other. When pollution causes harm to one organism only, this process can start a chain reaction and danger the entire aquatic habitat. When the proliferation of newly introduces nutrients evoke plant and algae growth, oxygen levels in the water decrease. This process, known as eutrophication, suffocates plants and animals and leads to dead zones i.e. water habitats without any life. Chemicals and heavy metals from industrial wastewater are also toxic to aquatic life. They can shorten an organism's life span and its ability to reproduce while also endangering humans, since humans may feed on these organisms and any toxic impacts on these organisms may adversely impact humans.