The Landwasser is a 30.5-kilometre (19.0 mi) river in Switzerland, canton of Graubünden. Its origin was Lake Davos before this was turned into a reservoir for a power station. Nowadays it is fed entirely by Flüelabach and changes its name near Davos. Davos is the largest town and except for the last bit the only municipitality on the river. This reflects the size of the municipality that was the biggest in Switzerland until 2011 the whole canton of Glarus was reduced to only three remaining municipalities.