Complex sentence: The Watauga River flows generally north and then west into Carter County where it forms the northern border of Elizabethton, Tennessee, where the Watauga then receives the flow of the Doe River.
Split into simpler sentences: The Watauga River flows generally north and then west into Carter County where it forms the northern border of Elizabethton, Tennessee. In Elizabethton it receives the flow of the Doe River.