Geropotamos in Rethymno is a long river that flows into the beach of Geropotamos, at the site of ancient Avlona, where it forms an important wetland. Its name means "sacred river", while near its exit it is also known as Avlopotamos due to the ancient city Avlona. Geropotamos gathers the waters from many tributaries on the northern side of Psiloritis.
Shortly before emptying in the sea, it joins with the river Margaritsanos or Mylopotamos, which owes its name to the many watermills that once operated along the way. Mylopotamos river gathers its waters from the area of Margarites and ancient Eleftherna. Mylopotamos is so important for the region that the entire province of Mylopotamos has been named after it.