(a) GENERAL RULES.-The Secretary and the Board have jurisdiction over transportation insofar as water carriers are concerned- (1) by water carrier between a place in a State and a place in another State, even if part of the transportation is outside the United States; (2) by water carrier and motor carrier from a place in a State to a place in another State; except that if part of the transportation is outside the United States, the Secretary only has jurisdiction over that part of the transportation