Cracking Dams: Problems with dams, b

What are some problems with dams? There are many good reasons to build dams, but there are also some bad things about dams. Place your mouse on each of the reasons.

Here is a scene of a dam failure () from the movie Asteroid*.	Used according to the Fair Use Doctrine
Although this is a make-believe story, there are stories of dams that actually cracked and failed in the Examples section.
What are dams made of?

What are some problems with dams?