What are the major environmental problems facing the global community today?
These are some reasons people build dams.
Dams decrease fish populations because they block fish migration. Dams caused 20% of global fish to become endangered or extinct. From the mid-nineteenth century to the late twentieth century, wild salmon populations have declined from 10-16 million fish down to 375,000 fish, resulting in a loss of $6.5 billion.
Dams block 98% of sediments from traveling downstream and contributing to fertile flood plains or coastal wetlands. This image of a dam being flooded shows how much sediment can be trapped in reservoirs.
Reservoirs caused by dams can cause large amounts of flooding and sometimes flooding cities, towns, or villages. Flooding caused by dams caused 400,000 square kilometers to be flooded and 30-60 million people to be evicted.
Dams cause changes in water chemistry parameters such as nitrate, dissolved oxygen, turbidity, and temperature, affecting the plants and animals of the ecosystem.
In this info-graphic created by Drew Overholser, the aspects of a global issue are displayed. River alteration is a global issue because it fits these qualities.