Swampy and inaccessible: Big Island. The river Iténez (for Bolivian) y Guapore (for Brazilian) represents the natural border between the two countries over 970 km. In this river, an island in the department of Beni is a tourist attraction as a very swampy area and not accessible all year durente, is not available all year, only in dry weather, which is between the months of June to December