The world needs a new source of energy, an unspillable source.

What are the byproducts in the process of electricity production in a hydroelectric power plant?

For our field trip, we had to visit a dam that was the primary source of energy for a hydroelectric power plant. We also have to answer a bunch of questions, and one of them is this:

What are the byproducts in the process of electricity production?

I tried looking for it in the Internet, but apparently my research skills aren’t that great yet.

I appreciate it, thank you!