After the overthrow of Rosas in 1851 the Parana was declared free for navigation to vessels of all nations by Argentine law and by treaties to which Brazil and Uruguay were parties, although Paraguay was not. Nevertheless, Lopez permitted ships to ascend freely to Asuncion. Lopez wished to concentrate all trade at Asuncion and opened no ports north of his capital. The upper course of the river belonged to Brazil, but the boundary between Brazil and Paraguay had remained unsettled from colonial times. In his control of the Lower Paraguay, Lopez had a lever to force Brazil to terms. He steadfastly refused to permit ships to ascend into Brazil in spite of the latter's persistent efforts to procure the natural and necessary right of egress to the ocean by an international river. While this matter still remained unsettled, Lieutenant Page of the United States Navy appeared in the _Water Witch_ at Asuncion on his survey of the Paraguay. Lopez was delighted, and extended every facility to the officer as far as the northern boundary of Paraguay. Page went on up to Brazil. Lopez was offended, for he feared that he would be at a disadvantage in his further negotiations with Brazil by having apparently granted to an American ship the permission which he had steadily refused to Brazilians. Unfortunately, just at this time occurred the quarrel with the American promoter, Hopkins. The American officer took his countryman's side, giving him refuge on board the _Water Witch_. This so enraged Lopez that he issued a decree prohibiting foreign war-vessels from entering Paraguayan waters, and one of his forts fired at the Lieutenant's vessel, killing a man. This outrage brought about Lopez's ears a naval expedition which compelled him to apologise and to agree to reimburse the Hopkins Company. Brazil also sent a fleet up the Parana to coerce Lopez into granting free transit along the Paraguay, but he cleverly held the Brazilians in parley until he had an opportunity to fortify the river. England's gunboats at Buenos Aires virtually held the Paraguayan flagship, with Lopez's eldest son on board as hostage for a young British subject named Canstatt, who had been imprisoned and condemned to death for complicity in a conspiracy at Asuncion. Lopez was forced to release him and pay damages.