identify 1 desirable consequence and 1 undesirable consequence. of using hydroelectric power for electricity?

Answer 1

This sounds like a Homework question. :) The obvious desireable consequence is electricity generated without any harmful side effects (oil and coal cause pollution, nuclear generates nuclear waste fuel).

The not so obvious undesireable effect is that dams often destroy rivers and the habitats of those animals (mostly fish, but sometimes other wildlife) around them. Additionally in crowded areas like China, it can cause entire villages to need to be relocated due to the lakes created by the Dam. (See Three Gorges project)

Answer 2

1 desirable consequence would be the reduction in pollution from coal fired generating plants.
1 undesirable consequence would be the further damming of rivers, which can negatively effect fish populations and in some cases cover historically or culturally significant sites.

Answer 3

Desirable: It is a renewable energy source that produces no toxic waste, including no global warming.

Undesirable: It can kill fish, flood good land behind the dam, and generally disrupt the natural river environment.