The Madeira river rises more than during the rainy season, and ocean vessels may ascend it to the Falls of San Antonio, near Porto Velho, Brazil, above its mouth; but in the dry months, from June to November, it is only navigable for the same distance for craft drawing about of water. The Madeira-Mamoré Railroad runs in a loop around the unnavigable section to Guajará-Mirim on the Mamoré River, but is not functional, limiting shipping from the Atlantic at Porto Velho.