Governors Island is a 172-acre ( 70 ha ) island that lies on the Upper New York Bay , about one-half mile ( 1 km ) from the southern tip of Manhattan Island and away from Brooklyn by Buttermilk Channel . Governors Island is a 172-acre ( 70 ha ) island in Upper New York Bay , approximately one-half mile ( 1 km ) from the southern tip of Manhattan Island and separated from Brooklyn by Buttermilk Channel .