Given the task definition and input, reply with output. In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

The Samborombon bay is found at the mouth of this river, and the Matanza river empties into it. On its northern bank lies the city of Colonia del Sacramento. Its navigable part is called the Canal Punto Indio, and the Isla Martin Garcia is also located in this river. The province of Entre Rios is located at the formation of this river near the confluence of the Uruguay and the Parana rivers. For 10 points, identify this river, which forms a big estuary at its mouth in the Atlantic, and on whose banks lie Montevideo and Buenos Aires.
Social Science