Manaus sits at the meeting of the Rio Negro and the Solimões, and boats are the main way to reach much of the surrounding Amazon. The main passenger terminal is the Estação Hidroviária, on the waterfront downtown, where slow boats depart for Belém (about four days), Santarém (roughly 36 hours), Tabatinga on the Colombian border (about a week), and dozens of smaller river towns.
For most routes you sling a hammock on the open deck — bring your own or buy one cheaply in the market near the port. The hammock deck fills up, so arrive early to claim a good spot away from the engines and near the rail. Cabins with bunks are available on the larger boats for roughly double the hammock fare. Food is included on most long-distance services, but it is basic; bring snacks and plenty of water.
Speedboats (lanchas rápidas) cut travel times dramatically — Belém in about 18 hours, Santarém in around 12 — but cost several times more and you miss the slow unfolding of the river. For day trips into the flooded forest or to indigenous communities, tour operators along the waterfront arrange motorized canoe excursions, though you will get a better deal booking through your guesthouse rather than at the dock.