For 10 points, name this Alpine lake fed by the ► Rhine which borders Switzerland, Austria and Germany, and shares its name with the 1414 church council that condemned Jan Hus and ended the Great Schism.
The cities of Hard and Horn lie on opposite sides of this body of water, which receives water from three streams called "Ach" that flow from Stockach, Dornbirn and Bregenz. Walafrid Strabo was the abbot of a monastery found on its Reichenau Island, and a former prince of Sweden, Lennart Bernadotte, owned its Mainau Island. Friedrichshafen is the chief port of this lake, which the sub-national entities of Vorarlberg, St. Gallen and Thurgau border. For 10 points, name this Alpine lake fed by the ► Rhine which borders Switzerland, Austria and Germany, and shares its name with the 1414 church council that condemned Jan Hus and ended the Great Schism. 
The cities of Hard and Horn lie on opposite sides of this body of water, which receives water from three streams called "Ach" that flow from Stockach, Dornbirn and Bregenz.
Lake Constance [prompt on Austria before "Horn" is read]