A part of the border between Austria, Switzerland and Germany may be seen from orbit.
For the biggest part of the Lake Constance, the Upper Lake, the location of the borders within the water is not defined. Therefore the lake itself is the border, a very wide one, easily to be seen from orbit at day and night.
Within a smaller part, the Lower Lake, the border within the water is defined.
See Wikipedia for International borders of Lake Constance or this chart of the Bodensee.
Another part of the border between France and Germany is the river Rhein between the towns Basel and Karlsruhe, see this chart.
