Final answer:
The Rhine River is filled by Lake Constance as it passes through Switzerland, Germany, and Austria.
Step-by-step explanation:
The Rhine River is filled by Lake Constance as it passes through Switzerland, Germany, and Austria. Lake Constance, also known as Bodensee, is a large freshwater lake located at the northern foot of the Alps. It is an important source of water for the Rhine River and plays a significant role in the region's economy and tourism.