A river's final destination is the ocean. An estuary is where the river's freshwater meets the salt water of the sea. Think about where you live. The sip of water you drink today could be the same water a dinosaur drank millions of years ago. Water flows around us in one great cycle.
Water falls to the earth when it rains or snows.
Then it evaporates from rivers and lakes and rises into the air to form clouds. When those clouds get full enough, it rains again and the cycle begins anew. This is called the hydrologic cycle or the water cycle. Watch a movie about the water cycle Earth movers Rivers carry more than water. Rivers are like big conveyor belts.