Environmental Impacts of Dams

Impacts on Fish

• Dams are created in order to change the currents of a River.
• Changing the current has an immediate impact on the ecosystem in the river.
• The dam changes the water qualities to which organisms are used to
• Many animal's life cycles are synced with the annual floods that occur in an area; therefore, those cycles are interrupted when the floods stop because of the dam
• The dam basically acts as a barrier stopping fish from going upstream or downstream; thus, lifecycles of migratory fish are deeply damaged, as they cannot go and spawn or interact with others.

Soil Erosion Before the Dam

• The sediment that the water carries is blocked by the dam; as time passes, it slowly builds up, adding additional pressure to the dam wall
• In this way, serious accidents can occur: the dams are only built to withstand a certain amount of water pressure; with the pressure from the sediment in some time the wall either explodes or water is caused to go above the dam, creating a waterfall; in both cases, a lot of organisms, including humans are in great danger.

Soil Erosion after the Dam

• As sediment coming from the upper parts is blocked, the water after the dam is essentially "cleared" of all particles
• Once again, that interrupts the ecosystem present
• The nutrients are blocked along with the sediment
• The organisms that used the mud to hide themselves now have no protection from predators.

Disease Spread

• The water that is blocked by the dam stays in one place, and, consequently, can get very dirty
• It attracts mosquitoes and other disease-carrying insects, which contaminate it

People Displacement

• When dams are built, the settlements and habitats that stand in their way are generally demolished
• This way, a lot of people are left without a home and a job, which is a big economical problem.
• The water is a breeding place for snails carrying the parasite bilharzia, which is the second worst disease after malaria in Egypt.

Other Environmental Effects

• The physical environment is altered
• Cycles and variation of flow downstream are effected
• Standing water (reservoir) habitats replace flowing water habitats
• Nutrients are unable to move downstream
• Reduction of biodiversity occurs
• Ocean fish migrations are blocked, most notably the salmon and steelhead