The building of a dam generally has a major impact on fish populations:
migrations and other fish movements can be stopped or delayed, the quality, quantity
and accessibility of their habitat, which plays an important role in population sustainability, can be affected.
Fish can suffer major damage during their transit through hydraulic turbines or over spillways.
Changes in discharge regime or water quality can also have indirect effects upon fish species.
Increased upstream and downstream predation on migratory fish is also linked to dams, fish being delayed
and concentrated due to the presence of the dam and the habitat becoming more favourable to certain predatory species.