an international border lies between countries
The entire Mississippi River watershed, except the Red River of the North whose waters ultimately reach Hudson Bay, and the Great Lakes which ultimately drain out through the St. Lawrence River and seaway to the Atlantic Ocean. (The Louisiana Purchase territories.)
India and Nepal
The channel lies between modern day England and France. It is about 350 miles wide.
Panama and costa rica
The Gulf of Bothnia lies between Sweden and Finland.
The English Channel lies between the UK and France.
The English Channel lies between England and France. In French, it is referred to as 'La Manche' (Translation - the sleeve).
asia
Gulf of Bothnia.
Between Austria and Switzerland
The Tasman Sea does not cross any countries. It lies between Australia and New Zealand.