chemtrails

I've wondered about these before but not to the chemtrail conspiracy level...what ARE these things and why on earth do we have DOZENS of them over the skies of Bozeman everyday?

A reporter for the Northwest Liberty News in Kalispell recently captured a striking number of contrails from airplanes in the area. He, however kept referring to them as "chemtrails". Although there WERE several crisscrossing the beautiful blue sky, I was under the impression that those visible lines were essentially water vapor. Your thoughts?