A TRIBUTARY is a freshwater stream that feeds into a larger stream, river, or other body of water. The larger body of water that a tributary flows into is called the mainstem. Tributaries do not flow directly into the ocean.
The map above shows the Salmon Falls River watershed and the many tributaries that flow into it. The Salmon Falls River is a tributary of the Piscataqua River which flows into the Gulf of Maine.
Tributaries carry runoff and seasonal meltwater to larger rivers. These tributaries can also be called headwaters. The point where a tributary meets a larger river is called the confluence.