A watershed is an entire river system—an area drained by a river and its tributaries. It is sometimes called a drainage basin. Hence, it is because, the Mississippi watershed has not been absorbed by the ground.
The Mississippi River
The Mississippi River can be divided into three sections: the Upper Mississippi, the river from its headwaters to the confluence with the Missouri River; the Middle Mississippi, which is downriver from the Missouri to the Ohio River; and the Lower Mississippi, which flows from the Ohio to the Gulf of Mexico.
Therefore, the reason is that it has not been absorbed.
learn more about The Mississippi River: https://brainly.com/question/1904174
