Common Carp

I checked out some web sites regarding warm water fish in Colorado. They generally focused on bass and panfish, but one site focused on common carp. I did not find any other large native or non-native minnow species that might occur in Colorado (at least none with scales like your photo).

That's what I was thinking too, but it seems so general-shaped that I just wanted to try narrowing it down.

It seems like a carp to me.

The fish was sticking it's head out of the water, splashing around and maybe laying eggs.

Possibly Common Carp (Cyprinus carpio)?

Could you describe it's behavior any? Had you seen it feed, or if it stuck its head completely out of the water or anything?