Location, location . . . what a location!

Having glided many times in a silent double-decker Swiss train along the western edge of the strange-colored yet beautiful Walensee, I was very interested to read Nico Saieh's post on this terrific house, designed by k_m.architektur, which is poised over the lake with a panoramic view of it. Nico's post is on Arch Daily, which is always good reading.

Next time I take that train ride I'll try to tear my eyes away from the stunning scenery and try to spot this house! – GF

Question: Does anyone know what makes the Walensee such a strange blue? I did some feeble research, but found nothing.