<P> The Mississippi River is called the Lower Mississippi River from its confluence with the Ohio River to its mouth at the Gulf of Mexico , a distance of about 1,000 miles ( 1,600 km ) . At the confluence of the Ohio and the Middle Mississippi , the long - term mean discharge of the Ohio at Cairo , Illinois is 281,500 cubic feet per second ( 7,970 cubic metres per second ) , while the long - term mean discharge of the Mississippi at Thebes , Illinois ( just upriver from Cairo ) is 208,200 cu ft / s ( 5,900 m / s ) . Thus , by volume , the main branch of the Mississippi River system at Cairo can be considered to be the Ohio River ( and the Allegheny River further upstream ) , rather than the Middle Mississippi . </P>
<P> The Mississippi River is called the Lower Mississippi River from its confluence with the Ohio River to its mouth at the Gulf of Mexico , a distance of about 1,000 miles ( 1,600 km ) . At the confluence of the Ohio and the Middle Mississippi , the long - term mean discharge of the Ohio at Cairo , Illinois is 281,500 cubic feet per second ( 7,970 cubic metres per second ) , while the long - term mean discharge of the Mississippi at Thebes , Illinois ( just upriver from Cairo ) is 208,200 cu ft / s ( 5,900 m / s ) . Thus , by volume , the main branch of the Mississippi River system at Cairo can be considered to be the Ohio River ( and the Allegheny River further upstream ) , rather than the Middle Mississippi . </P>
where does the mouth of the mississippi river start
where does the mouth of the mississippi river start
Gulf of Mexico
Gulf of Mexico