How do building dams for electricity affect ecosystem someone me

The first effect of a dam is to alter the pattern of disturbances on which the plants and animals of a river depend. Many aquatic animals coordinate their reproductive cycles with annual flood seasons. Every flood is valuable in that it takes nutrients from the land and deposits them in the river, providing food for the stream's residents. Floods also provide shallow backwater areas on vegetated and shaded riversides; the young of many animals depend on these backwaters to protect them from predators too large to swim in these shallow waters.

Idk i think the answer choice is number 1