Complex sentence: The Wateree River, about 75 mi (120 km) long, is a tributary of the Santee River in central South Carolina in the United States, which flows to the Atlantic Ocean.
Split into simpler sentences: The Wateree River is a river, about 75 mi (120 km) long, in central South Carolina in the United States. It is a tributary of the Santee River, which flows to the Atlantic Ocean.