Flathead Lake is an enormous freshwater lake in the northwest part of the Treasure State that also happens to be the clearest lake in Montana -- and one of the clearest lakes in the entire world!

Of course, the main feature of the Flathead Valley is Flathead Lake. It's one of the largest freshwater lakes in the country, and it's famously crystal clear. The lake water is among the cleanest in America, thanks to low levels of algae.