Final answer:
Dams can have both above and below hazards, affecting the natural water habitat, fish migration, and populations.
Step-by-step explanation:
Dams can pose hazards both above and below them. Above the dam, the creation of reservoirs can lead to environmental impacts such as changes in water temperatures, chemistry, flow characteristics, and silt loads, which can affect the natural water habitat and the ecology of the river. Below the dam, migration of fish can be obstructed, and fish traveling downstream can be killed or injured by turbines in the dam. The flooding caused by reservoirs can also result in the displacement of populations and the loss of habitats.