The River Isère is a river of southeastern France that flows through the Rhône-Alpes region. It is a tributary of the Rhône River, which is also located in southeastern France. The Isère River is approximately 200 kilometers long and is an important source of hydroelectric power. The Rhône River is the second longest river in France and is approximately 812 kilometers long. It flows through Switzerland and France and empties into the Mediterranean Sea.