Complex sentence: The river was once navigable by ship up to the city of Nacimiento, however over-logging during the twentieth century led to heavy erosion that choked the river with silt and rendered it impassible to ship traffic.
Split into simpler sentences: The river was once navigable by ship up to the city of Nacimiento. However, over-logging during the twentieth century led to heavy erosion that choked the river with silt and rendered it impassible to ship traffic.