What is the primary negative effect of dam-building?
a. dams prevent flooding of only small areas.
b. dams disrupt the delicate ecology of an area.
c. dams remove sediment from river beds.
d. dams keep fish from breeding.

The correct answer is - B. Dams disrupt the delicate ecology of an area.

The dams are very useful for the humans, but hey are very damaging to the ecological systems. When a dam is built, it is immediately restricting the organisms to move freely, thus they have restricted movement only to a certain are. They also contribute to the temperature of the water, and as the water is becoming more stagnant, it is getting warmer, thus effecting the organisms that are adopted to different temperature of the water. The breeding can also be restricted because some species only reproduce in certain places, and the dams often don't allow them to move there.