Explanation:

Potomac River is found within the Mid-Atlantic region of the United States and flows from the Potomac Highlands into the Chesapeake Bay. In terms of area, this makes the Potomac River the fourth largest river along the Atlantic coast of the United States and the 21st largest in the United States.
Seine River is a river in Kenora, Rainy River and Thunder Bay Districts in northwestern Ontario, Canada.
Manzanares is a river in central Spain, which flows from the Sierra de Guadarrama, passes through Madrid, and eventually empties into the Jarama river, which in turn is a tributary to the Tagus .
Hudson River is a 315-mile river in New York. It had previously been observed by Italian explorer Giovanni da Verrazzano sailing for King Francis I of France in 1524, as he became the first European known to have entered the Upper New York Bay, but he considered the river to be an estuary.